Inspired by Geoff's torture by Pepsi with a lemon wedge.
Mine was when a friend was staying with me for a conference. We went out for really spicy Thai food and got hammered. While we were walking into town the next morning, my combined hangover/chilli guts got the better of me.
It was the worst possible point on the walk - almost exactly halfway between home and the nearest other toilet. I chose home, and trotted back with my teeth and cheeks clenched.
I was living in a flat above a medical centre. By the time I got home I knew I wasn't going to make the three flights of stairs up to the flat, so dashed in to the medical centre toilet instead.
I was so desperate for cheeks to hit seat that I tore off a belt loop. Photo finish, but I made it. I made it.