Dom Joly: My 82-year-old mother-in-law thinks I'm a square

It was all going to be so rock' n'roll. A friend of mine in the States organises a huge free festival at the gloriously named Merriweather Post Pavilion in Maryland. Some of my favourite bands were booked, the weather was scheduled to be good and I had an "artist" pass that allowed me to wander anywhere I wanted. What could go wrong?

Well, the date was the first problem. It was gently pointed out to me that the festival was on the day after my daughter's 10th birthday. So I procured two more passes and my wife and daughter were now to accompany me. Then, another call, this time from Canada: my 82-year-old mother-in-law, excited we were coming to the US, was coming down to join us. I wangled one more pass.

On the day, we hopped into our rather rock'n'roll black Escalade in DC and headed off to Maryland, with me wondering if I could dump everybody in a trailer and then go ligging to my heart's content. I decided to play it by ear. We arrived and hopped out of the Escalade. The heat was overwhelming, 38C and 90 per cent humidity. I started to wilt. We made our way through the throng of festival-goers, trying to find the backstage area and, hopefully, some shade.

The first two bars I saw looked to be populated solely by polo shirt-wearing banker types – possibly the only people who could afford the astronomically expensive alcohol. However, the backstage area, to my delight, had a free bar. We had a couple of mojitos and sat by a little lake in an area that looked not unlike a hillbilly sitting-room: random sofas and chairs dotted around a couple of ramshackle fire-pits.

The heat was getting unbearable and I was really starting to feel the effects. I looked around, assuming my family were going to be feeling a lot worse. But my daughter was happily playing with some kids from one of the bands, while my wife and mother-in-law were tucking into the Mojitos and starting to look like they were close to dancing. I just felt hotter and hotter. I mumbled some excuse and left the garden. Outside was a huge table on which somebody had poured an ocean's worth of seafood. It looked like some marine holocaust – huge crab claws, prawns, oysters all gently cooking in the baking sun.

The smell hit me hard and I felt nauseous. I ran for the loos. Ten minutes later, and about a stone lighter, I stumbled back into the garden where my mother-in-law and wife were both dancing with what looked like several members of the Manson family. "This is Edward Sharpe and The Magnetic Zeros," shouted my wife, as they danced off into some woods from where heavy techno blared.

"I've got to go," I said weakly. "I'm not feeling well...."

The family peeled away from the Mansons to look at me in shame.

"You want to go back to DC?" asked my wife in a faintly disgusted manner. "We're having a great time," whooped my mother-in-law, as she necked what seemed to be a pint of mojito.

I felt nauseous again. My daughter was now playing with a pitbull that belonged to someone in Pavement. I was getting weird flashes.... had somebody spiked my drink? I insisted we leave. The family clambered back into our Escalade and we headed back to the US capital in sullen silence.

"You have good time, everybody?" asked our Egyptian driver.

"We were, until somebody decided to stop it," my wife mumbled.

"Yeah, my daughter married a square," said my mother-in-law.

It's not easy, being a dad.