1. Something you say when something is funny, usually when someone gets hurt is a good time to say it.
2. The act of putting your arms straight out at an angle then rotate them up and down (like a see-saw) while spinning around in circles as fast as you can. With your arms out like this you can spin much faster than normal and usually fall. Warning: only do the rolfcopter manuver when in an open area for less risk of injury.
Tom - "Dude how did you mess up your hand like that"
Caleb - "I was doing a roflcopter in the yard and hit it on the fence"
Tom - "HAHA roflcopter!"