The older person's guide to Eminem

When I first went to the Reading Festival in 1978, I was working at the telephone section of the Post Office, surrounded by the sort of people who say "Last night the phone rang at 10 past nine. I turned to Bob and said 'Who's that ringing at this time of night'?"

But for three days we roared at the bands, gloried in the squalor and reached that misty, drunken, stoned stupor in which the answer to any question is an elongated "Eeweugh" that tapers out before the end. Followed by a five-second pause and a guttural "Huh, huh, huh" as if that was a particularly witty "eeweugh". And there was Tom Robinson and The Members and Patti Smith and my mate was arrested for slashing up a wall in the town centre and the next day he was fined 15 quid. Perfect.

This Sunday the atmosphere seemed remarkably similar, except I was sure there were groups of first-time festival-goers peering my way and muttering "I wonder what that old bloke's doing here – must be the police". One woman in her forties with five nose rings and a stud through her lip had no qualms about dancing through the first song of the first band by shaking maniacally like a dog as it leaves the sea. Then she said to her daughter of about 10 in a delightful suburban mumsy voice "Jeanette, if you can't behave I'm taking you home and you won't see Eminem."

The band was on in one of the tents away from the main stage, and began at 11.30am while most of the audience sat cross-legged on the floor staring into the middle distance. Unperturbed, they thrashed through a series of invigorating punk riffs while the singer screamed in magnificent rage, and you couldn't help but be impressed that anyone could be that cross that early on a Sunday. It was impossible to work out what any of this was about, which added to the thrill, but then the singer introduced one song by saying "This next one is all about my school sports day." Then the riff and two more minutes of fantastic indecipherable wrath. What could the lyrics have been? Perhaps "I won that bastard sack race / But they gave the prize to Jones instead / And now I hope the bastard's dead"?

But it's all so wonderfully heartfelt, and rather than be cynical about the earnestness, it seems more positive to rejoice in the passion. Because the over-riding joy of a festival such as Reading is that it's naughty. Just as it was back in '78, it still feels naughty to sit openly in circles rolling joints. It's naughty to make mini-fires out of discarded lager cartons. Even the toilets are naughty. The whole thing would be ruined if they had marble tiles and John Coltrane playing through the speakers. Or even if they had paper, or bolts on the door or someone clearing up the five inches of alarmingly coloured water that slushes across the floor. Your parents would be disgusted, and that's the appeal.

In the afternoon it rained. Of course it did. And that's when it's so heartening to be at Reading. Because no one says "Ooh dear, isn't it terrible?" Or "Tut, and they said it would be mild on the forecast." No one half-smiles and informs you that at least it's good for the garden. Possibly because if you've lived for three days in a swamp without washing, and collecting leaves to use as toilet paper, you're not likely to go "Uugh, now I've got rain dripping down my neck – that's disgusting."

Over in the Radio 1 tent were rappers Mark B and Blade, who asked the women to yell on their own, and then the men, to see which could yell the loudest. They're supposed to be rappers and they're doing stuff you'd expect from June Whitfield in Puss in Boots at the Guildford Civic. Maybe that's how they'll end up, as the first rapping Aladdin, shouting "Oh no it's my wicked aunt, but she shan't be so bad if you chant 'Oh no you can't'."

Like me, I suspected that most of the crowd was eagerly anticipating star attraction Eminem, so it was a little unimaginative for the organisers to fill the six hours that preceded him with a tiresome procession of American thrash heavy metal. From the main stage, one fat bloke after another announced in a booming gravely mid-West accent "We are (whoever) and WE MOTHERS SUCK!" One consequence of this billing was to make the festival one of the whitest musical events imaginable.

As well as that, am I getting old or didn't heavy metal used to have a tune? Smoke on the Water, Paranoid – these were songs you could hum along to. Most notable amongst Sunday's acts were Queens of the Stone Age, who excelled in every heavy metal cliché (interminable guitar solos, long-haired spitting drummer, frequent angry screams of "I said are you mothers ready to rock?"). But they did add one innovation which was that the bass player played the entire set stark naked. About 10 minutes in, one fan climbed onto his mate's shoulders, under the camera that was displaying crowd scenes onto a huge screen, and stripped down to his underpants. At which point 20,000 people thought "Yes, that is a display of exhibitionism I suppose. But did you not consider it might be somewhat undermined by the fact the bloke on stage playing bass is completely bloody starkers?"

At one point the lead singer announced a new song, never previously performed called "Keep Your Mouth Shut". And the hardcore fans cheered, as if they were delighted their heroes were taking up a worthy cause, thinking "At LAST someone's prepared to speak out on this issue. For years the music industry has been afraid to tackle the problem of open mouths, but not Queens of the Stone Age."

Finally the naked bass player smashed up his guitar, which would have been all right but the keyboard player set fire to the smallest of his keyboards. "Yeah, yeah" he screamed as he pointed to it but the flames just sat on the top like they do when you set fire to a Christmas pudding. Then, after about five seconds he covered the flames with a damp towel, as if he was demonstrating how to deal with a fire in a frying pan. And so as great rock'n'roll moments go it was on a par with the night Ready Steady Cook featured a flambe dish from Anthony Worrall-Thompson.

Eventually, every gap in the field closed and the hush of anticipation grew in the wait for the rapping hero. A glimpse across the colourful scene was a reminder of the limitations of Festival naughtiness. On one corner stood the bright Bacardi Breezer dance tent, on another the Carling Black Label tent. In the minutes before Eminem's appearance, the screens displayed huge adverts for cars, banks and mobile phones. And somewhere sat Vince Power, owner of the site and reputed to be worth £30 million.

Then on he came, a little slow at first, possibly because it's hard to get a crowd to sing along in that community festival way with rap. Sure, The Eagles have no problem getting 20,000 salesmen in jeans to hold lighters in the air and croon to "Hotel California", but it's not as straightforward when the lyrics go "If I'm going to stick it to anyone in showbiz, it'd be Jennifer Lopez, and Puffy, you know this."

Amidst the mainstream hysteria that's surrounded him, his opponents appear to have missed one of the main reasons for his popularity – that he is a fantastic rapper. He pelts out rhymes like these at astonishing speed with perfect clarity, which makes me wonder why he isn't a hit with my parents' generation. They were always telling us the marvellous thing about the old-fashioned singers was "you could hear all the words". So shouldn't they be stacking him up next to the box set of Frankie Vaughan?

In many respects the musician he resembles the closest from pre-rap days is Bob Dylan, with a similar mastery of rhyme, and jangly cheerful tunes masking macabre stories. But then one of his band came on, yelling "Hey, Slim, guess what? I've just been given some tabs of ecstasy." "Shall we drop them?" announced Slim, and got the crowd to chant "Drop the pill, drop the pill." Suddenly, the target of respectable Western society was acting out a stupid scene that looked like something from WWF wrestling on American telly. So he swallowed what was probably a tic-tac to huge cheers, then went off for an interval, during which the screens displayed a cartoon called The Slim Shady Show incorporating the characters from South Park. Maybe someone feels his audience is so young they can't go an hour without a cartoon. Next year he might break up his set with an episode of Blue Peter.

Then he was back to deliver more of the genuine rage that makes him popular with so many 18-year-old angst-ridden fans. For it's not the anti-gay material that attracts most of them, but the passion, as powerful an expression of feeling rock bottom as can be found in the finest blues. Part of that persona is a cartoon bravado, that had him and 20,000 others singing "Never go out without your pistol." But as I watched the curly-haired lad with glasses next to me pelting this out, I couldn't help feeling he wasn't likely to follow this up when he got back to his parents' house in Basingstoke.

Eminem's appeal is the same as that of the whole festival; he's naughty. It's naughty for a huge crowd to sing "I was high when I wrote this so suck my dick." In a world apparently dominated by passionless suburban twaddle like Changing Rooms and pension plans, he makes teenage anger legitimate. As you get older, you can't pretend events such as the Reading Festival speak to you in the same way they did when you were 18 yourself. But you can glory in the mud, get pissed, afford a cab back home to your warm functional toilet, and not get disillusioned in five years time when BBC1 viewing on a Bank Holiday afternoon is Eminem on Ice – Live from Earl's Court.