Few I've had:
Had an accident on my 600 hornet, so was given a bandit 650 as a hire bike. First bike with a centre stand, and was also a heavy bastard compared to the hornet. Standing in a petrol station (back against the pumps), put it onto the centre stand. Except what actually happened was my foot slipped out on diesel. Rather than drop the hire bike, I decided to pull it towards me, which basically resulted with me sitting against the pumps with the bike pinning my legs down. I can't move, and the only chap around was a tiny little old Chinese guy, who managed to lift the bike just enough that I could wriggle out and lift it up myself!
Second one, 125 battery was flat one winter, so I decided to bump start it. Foot slips on ice as i'm running along and my hand slipped off the clutch so it fired, and promptly pulled me straight into the back of my neighbours car, putting a nice big tyre shaped dent in the rear.
Third one, just fitted hard panniers to the hornet that stuck out a fair old way. Went to park in my local ASDA car park (which has bollards around the bike bays). Girlfriend on the back says "it won't fit" - I completely forgot about the panniers and so went straight into the bollard. Pannier was fine, but the bike got dropped onto the bollard on the other side, putting a big fat dent in the tank and jamming the bloody thing in between the two!