Once, when learning to ride, I came up to a stop sign and forgot to put my feet down. Managed to save the bike and not drop it, but it was ugly.
Spent 20 minutes troubleshooting why my bike wouldn't start when it clearly had gas and spark, only to see the kill switch in the stop position.
I also got a story that I wouldn't believe if it didn't happen to me.
A few months ago, my dad bought a couple of Honda Trail 70s. Fun little bikes. Anyway, we were getting one running and it was running a little rich. We were tuning the carb and fiddling with it. It was hard to start (kickstarter pawls were worn) and the best way to start it was to put it in top gear and have a friend push it while you held wide-open-throttle (and choke if cold).
Well my brother (and I) have a habit of wiping our hands on our shirts and pants when working on machinery. We had been dealing with carbs all day and has been wiping gasoline-soaked hands on ourselves. By the end of the day, our shirts could be classified as a petroleum-spill disaster area and FEMA called in.
Anyway, the little bike had a habit of "loading up" on fuel during the "takeoff run" and when the engine caught, it would bark fire out the exhaust for the first few dozen yards. (No flame arrestor in the silencer) Rather impressive at night. Well it was getting into the evening (getting dark) and I had just re-set the needle jet to run a bit leaner so we were doing a test run. I was piloting the bike and my brother was pushing me. We were tired and had forgotten about the engine's fire-breathing ability.
Top gear
choke off
full throttle
ignition on
GO!!!
After about 75 feet or so, the engine caught and with a BANG! it spat an impressive three-foot flame out the back. Right into my brother's gasoline-infused shirt and hands.
I hear this massive YOOOOOOOWWWWWWWW!!! come from behind me and see him frantically trying to put the front of his shirt out with his flaming hands.
I drop to first gear and immediately spin the little bike around to go help. However, if you don't know, the first gear in the Trail 70 is a hill-climbing gear and is VERY short. I romp the throttle and the front wheel picks up in an unintentional wheelie.
My dad said it was the funniest thing he ever saw. My brother, who was on fire, finally got himself put out right as I ride past him, shocked look on my face, doing a wheelie and right as I got past him, I let off the gas and fell forward and off the bike.
The upshot? No damage to the bike, myself or my brother. And we did learn the practical value of Flame Arrestors in off-road bikes. My dad laughed his ass off too.