pee (one's) pants
1. Literally, to urinate while still wearing one's clothing. I need you to pull over the car right now, or else I'm going to pee my pants!
2. To laugh in a hysterical or uncontrollable manner (i.e., to the point where one might actually urinate in one's pants). Wow, that standup comedy was great! She had the audience peeing their pants!
3. To be absolutely petrified with terror; to be scared out of one's wits. I was peeing my pants when that huge burly guy started threatening me and my girlfriend.