The 2 Live Crew song "Face Down Ass Up" pretty much describes the  position Luther Campbell finds himself in right now ... because the Tax  Man's about to rip him a new one.Campbell -- famous for the 2LC hit, "Me  So Horny" -- just got slapped with a $74K federal tax lien.According to  IRS docs -- obtained by TMZ -- Luther didn't pay either all or some of  his 2012 taxes.Campbell famously fought the government once before and  won ... after a federal appeals court threw out a ruling by a lower  court judge that the group's album, "As Nasty As They Wanna Be," was  obscene.