1. The act of being repetitively struck on the anus with devastating force.
2. Before preforming anal sex with a back door virgin, you spank her rectum to "tenderize" or "loosen" the anus for easier penetration
1 ex. "Yea man, last night at dinner Hillary got me Sphincter Slapped when she told my parents about my herion addiction."
2 ex. "While in bed with Hilary the other day i flipped her over and Sphincter Slapped her for anal preparation."