wet one's pants

Meanings

1. To wet oneself, to urinate in one's clothes while wearing them.
2. To laugh uncontrollably.
3. To be afraid; especially, to be extremely afraid.

Etymology

The senses referring to laughing and being afraid are extensions from the literal (urination) sense; both involve an element of variably literal or figurative nature: they are generally figurative, but if one laughs hard enough or gets frightened badly enough, the wetting may sometimes happen literally.