The male equivalent to pms. When a man waits too long to beat his meat he becomes beat deprived. This generally makes the man irritable and much more susceptible to getting a boner.
Spencer had BD because he went on a family vacation and couldn't find the time to whack his shit.
Spencer's Mom: why is spencer so mad?
Connor: he hasn't beat his shit in awhile.
Spencer's Mom: what?
Connor: he has a bad case of BD/Beat Deprivation.