Not done many stupid things at school, bags of flour, tied up and launched at a group of little kids was awesome. Only happened once though, and not by me.
Someone took a BB gun in and shot a teacher in the groin.
Someone slapped a teacher's ass with a ruler as she walked past, and he got expelled.
Another kid put his finger through the flies of his trousers and told the receptionist the "Suck it" and he got expelled as she thought it was his dick.

Teacher threw a stool at a kid and hit him in the back with it, he shoved someone against some railings, called him a cunt and said he'd put his head through them lol.

I haven't got any stories of anything i did, as i'm a good boy, never had a detention before, oh my!