Loads of stuff in chemistry, bucket of water, fairy liquid, methane from gas tap, large fire ball, great fun untill one bit floated up the cieling and we decide to set fire to it, fireball spreads across ceiling round pc projector :) Thankfull didn't brake anything or set fire to building.
Did the thermite reaction under the heat sensor thing (got rid of smoke alarms for obvoius reasons), 2500 °C under heat sencer connected to fire alarm isn't a good thing really.
Allowing someone to record me down half a litre of beer at the end of a rather heavy evening becouse that ended in disaster.
First stupid thing i can remember doing ever was trying to slide a 2 person skibob round a corner to stop at the end of a rather large slope rolling the thing sending my mate over my shoulders, cut us up a bit.