When it comes to class clownery, it's all fun, games, and slightly irked teachers until things get taken a step too far. Thumb tacks on seats. poisoning a substitute's tea. Making a DIY stink bomb with cheese left in an air duct. There's a fine line between silliness and stupidity, a lesson several students wound up learning the hard way. 

From backfiring pranks to straight-up bullying, here are 23 times the class clown went too far, as told by their former classmates.