PMBWSEMY

is the acronym for:
Playing My Bass While Simultaneously E-Mailing You. Used when someone asks what you are doing, and you are either actually playing a bass, or in some circumstances, Masturbating.

You could also use PMBWSFYA.
PMBYSFYA stand for Playing My Bass While Simultaneously Fragging Your Ass, if you want to tell your opponent how crappy they really are.