A method of protecting your favoured place in a canteen. A pritt-stick, lid off, was hurled to the ceiling directly above your chair. The threat of non-toxic adhesive looming ever above would deter any pretenders to your plastic throne.
Leaving you to sit under it, instead. A mixed blessing.

We had one teacher who, on entering the classroom would close the door unneccesarily hard, possibly to make up for small or non-functioning genitalia. Having enjoyed sticking a generally disliked chap's pritstick to the ceiling as a form of bullying for some time it was decided by most of the class who owned pritsticks that we should prime a trap for the soon to arrive teacher. We managed to get approximately ten stuck just inside the door before our lookout ran into the class, clearly excited. We sat, to a man bricking ourselves, in silent trepidation. I could hazard a guess that i wasn't the only person who, seconds before detonation, wished i hadn't taken part, or wasn't even in the room. events transpired as follows:

1: Teacher enters the room, turns, slams door.
2: 4 or 5 pritsticks fall on and around him
3: Teacher goes spastic.

Its great looking back, but i genuinely feared for my life at the time. We all got detentions, even the kids who were too poor to even own pritsticks, the twats.