def1: infestation of the pubic hair by crab lice
def2: These crustaceans have a hard bony or chitinous outer covering with a small abdomen concealed beneath it, short antennae, and five pairs of legs, of which the anterior pair are large and pincerlike.
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.