Jonny McCambridge: The latest birthday party blunder...riding a bike on the River Lagan

There was the occasion where I thought it would be a fine idea to make balloon animals. The novelty caused a sensation and I needed to deploy other parents as crowd control as I was surrounded by an excited mob of tots screaming 'Elephant!', 'Monkey!, 'Lobster!', while I worked furiously twisting inflated latex and pleading, “I can only do a sausage dog!”

There was the year when we went to the adventure playground and the children improvised a game which involved trying to bury me alive in the ball pit (I can't breathe! I'm not joking!)

Then there was the trip to the park where a fun wrestling match descended into farce with 30 children piling on top of me while a small girl tried to stuff handfuls of grass down my throat ("It stops being fun, when someone gets hurt!”).

There was the go-kart racing track where I was lapped by several laughing children before crashing against the wall and suffering the indignity of having to be rescued by the disinterested attendant with long hair and acne.

Another year we sat in large inflatables circles and hurtled down a dry ski slope. Encouraged by my son, I slid towards a steep ramp and screamed 'Ooooowwww!” as the unhappy equation of girth, geometry and velocity resulted in me becoming airborne and doing an ugly impression of Evel Knievel attempting to jump the Grand Canyon.

And, just to prove that all of the hurt wasn't physical, there was the year we went bowling. As I watched, a little girl with glasses approached and asked if I was my son's "grandfather".

This year four teenage boys and I are on bikes. The novelty is that we are in the middle of the River Lagan. Hydro-biking is the choice for the latest method of torture.

After being given the safety briefing, we begin. My son and two of his friends quickly get the hang of it, but the other boy veers his bike into the bank and gets stuck. As the 'responsible adult' I decide it would look negligent if I did not stay with the marooned youth.

Soon, a young woman in a boat comes to free him. She then hooks his bike to the side of her motorised vessel and gives him a lift back to the main group.

The unfortunate result of this is that I am left well behind. The other bikes are now just dots on the horizon, like Christopher Columbus and his fleet disappearing off in the direction of the new world. I am alive to the potential taunts of the 'old man not being able to keep up' so rouse myself to greater effort.

I begin to pedal furiously. Soon the sweat is stinging my eyes but I am making ground. After 15 minutes of strenuous effort I have caught the main pack, who are travelling leisurely and chatting amiably. Absurdly, and in an ill-judged show of bravado, I glide straight past as they watch.

I keep pedalling and gasping, refusing to look behind. Eventually, the woman in the boat draws alongside me and points out that the rest of the party turned some minutes ago and are now heading back to base, while I seem determined to make it to Stranraer under my own steam.

I have to turn around. The obvious option of using the handlebars seems not to work. I turn hard left but the wind and current ensure that my vessel keeps moving to the right. Instead, I have to improvise a method of reversing a bit, then going forward, then back again until the bike is pointing in the direction I want to go; essentially a three-point turn in the middle of the broad, majestic Lagan.

The boys are now further off in the distance than ever. The kind woman in the boat asks if I want a lift, but I'm too proud and stubborn to accept. I raise my capacious backside off the seat of the bike and pedal harder than ever, like Eddie Merckx in the Pyrenees.

It is raining heavily. The sun cream I had applied is now running in streams down my face. It had been pointed out to me before that this activity was a 'unique way' of experiencing the sights of Belfast, but the truth is I can see and hear nothing beyond the furious pounding of my thighs.

It seems to take forever, but again I catch up with the boys. Again, they watch with curiosity as I pedal straight past. I have made it a personal obsession that I will be first to get back to base.

It is some minutes later when the woman on the boat again draws alongside me and points out that, like brave Odysseus, fate has blown me off course again. I have cycled straight past the point where we were supposed to return the bikes. The rest of the boys are already back on dry land while I seem to be heading towards the origin of the river in the distant Mourne Mountains.

Wheezing pathetically, I make another awkward turn and, with the last grains of my energy, return to base where the boys are waiting, cheering sarcastically. There is further indignity. As I climb off the bike, it becomes obvious that the strength in my legs has gone and I have to be supported to remain upright. Then, after peeling off the claustrophobic life-jacket, the sight of my sweat-drenched T-shirt clinging to my bowling ball tummy, is the source of endless merriment.

I have no energy left to protest. I take the boys for pizza. As they eat, I sit quietly in the corner sipping on a black coffee. They are already excitedly planning what they could do for the next birthday party.

I can’t wait.