1. Crabs: can be those tiny bug's that will infiltrate the pubis.
2. You can also describe a person for being being a Grumpy/Angry Shit.
1. damn those crabs *itch* so itchy *scratch*
2a): )"¤()#<insert naughty words>(="/%&/# *walks away*
2b): Now what was that all about?
2c): He had crabs up his bum or someone put crabs in the toilet when he went for a shit.