I usually figure that when they start looking for me they are too hot. :roll: They do occasionally when I've upset them, but they never tell me which hive they are from, so then it gets tricky.
If I stand by the hive and watch and they are headbutting me then somebody is going to lose her head!! :evil:
Keep in mind, though, that they are more testy when the weather is bad and they can't get out and forage.