Another particularly nasty one used to be to get a stick of AN60 Gelignite, cut it in half and rub the content (was like candle wax in consistency) on the sweat band of somebody's hard hat at work.
The person who owned the hard hat could not see or smell or detect the presence of the stuff in any way, but after wearing the hard hat for a short time, would suffer a headache best described as a migraine. Very nasty.
I've never done it, nor had it done to me, but I have seen the result of it being done to somebody else - and it isn't something I'd recommend.
I'm pretty sure that AN60 isn't around any more these days, but no doubt there's other similar compounds that would have a similar result.

