Abbreviation for "shit my pants" or "shat my pants." Can be used in a variety of situations, most notably whenever something's funny, shocking or horrifying. Also appropriate when referring to an attractive member of the opposite sex. Whenever it's unclear whether a situation is, in fact, funny, shocking or horrifying, it's best to use a qualifier, e.g. "that was S.M.P. hilarious," or, "that was S.M.P. tasteless."
"The lunch lady at the cafeteria is S.M.P. hot!"
girl#1: "What's that smell?"
girl#2: "I S.M.P.'d"
"When Malcolm busted ass on his skateboard, it was so funny I just about S.M.P.'d"
"My mom just about made me S.M.P. when she found me alone with the pet goat."