"Crabs" are a sexually transmitted disease, so when Tia has actual crabs coming up to her...it easily became a dirty joke.
When the little rock crabs went crawling up Tia's skirt at the beach scene, my best friend and I both turned and looked at each other and just started giggling, since we are also perverts and were like, "Tia's got crabs, tee-hee".
This greatly amused the people sitting around us, although I doubt we were the only ones with pervy minds, because there were lots of laughs at all the dirty jokes in the film
And there were tons of naughty jokes in this film, weren't there? Did any of the other films have as many 'adult' themed jokes as AWE? Now I'll have to go rewatch all three films. Oh darn...