Dom Joly: Give parents their happy hour on the bouncy castle

It's my son Jackson's fourth birthday today, and we're having a big party for him. Stacey has booked a huge bouncy castle for the south lawn, and boxes of going-away presents, dinosaur-related plates and other bric-a-brac has been overloading our poor postman. Should it rain, the village hall has also been rented as a fallback – nothing has been left to chance. Jackson is blissfully unaware of all Stacey's hard work. He is more concerned with the guest list. One moment he wants "no girls", then he wants "no boys". Invites change by the second, as someone becomes uninvited because they threw sand in his face or were "mean". In my experience it's best never to invite boys, as they are a total nightmare compared to girls at that age. I remember the first time my daughter Parker invited boys to her party – a little feral gang rampaged through our house hitting dogs with swords and shouting ... so much shouting.

I'm also now slightly concerned about the bouncy castle after the story of some kid who got paralysed playing on one and sued the parents who had hired it. I'm thinking of getting everyone who turns up to sign some sort of legal document that negates their right to sue us – I might even have a lawyer on site. Last year we had a piñata – a multicoloured donkey stuffed full of sweets that hangs from a tree while the kids bash it with a stick until it bursts. This was a total health-and-safety minefield as the donkey was regularly missed and the stick would scythe through the watching crowd of kids. We had about three black eyes before I stepped up and smashed the bloody thing.

My main job, apart from avoiding expensive lawsuits, is to get the parents drunk. Whenever I go to other kids' parties, the parents are never catered for. Mothers hover over their progeny like boxing trainers. Occasionally they will gather in groups and discuss the latest school gossip. I'm determined to get everyone plastered and on to the bouncy castle. I love bouncy castles, but they are always for kids. I'm going to have a private half-hour for adults – drunk adults. What could go wrong (barring the sort of freak accident we've read about recently)? Why no bouncy bungalows or bouncy tunnels? Bouncy castles only ever have three walls, with one side completely open. What kind of castle is that? Any besieging horde of infidels would storm it in seconds.

We have a particularly busy weekend as it's also our wedding anniversary. We have agreed on a mutual present of a Wii Fit game. This is an interactive video game where you do workouts that are "fun". No workout is ever fun in my experience. We have a personal trainer who tortures us every Sunday and I pray for a phone call every week saying that he can't make it.

I'm having to get in shape because I rashly agreed to present a travel programme in Nicaragua that had, hidden away on the schedule, the words – "Day three – climb volcano". I had to go for a medical for the programme insurers yesterday. It got slightly weird when the doctor pulled down my pants and started feeling my testicles. "Just checking for testicular cancer," he said cheerfully.

I had to take his word for it but felt slightly dirty as I got back into the tiny lift and headed downstairs. I took the lift because he was on the fifth floor – doesn't really bode well for the volcano climb... still, at least I'm all clear on testicular cancer. I must remember to bring this up with the mothers at Jackson's party.