Online chess is not the only place you will encounter this sort of thing. When I played in our national junior chanpionship (in 1973?) one of the players resigned by demolishing the position and throwing his King out the window. We were on the top floor of the building, so I hope nobody got hurt. It would look pretty odd on an accident report.
When I played in the Canadian Open (the following year?) one of the players "resigned" by kicking his opponent in the nuts and running away.
EDIT: It wasn't me, by the way.
Every other game I play my opponent leaves and lets the time run out when they are in a losing position. I always used to think chess was a gentleman's man.