The use of this term comes from the word (biscuit), meaning white boy, which no one other than white people can use without becoming very offended. The term (ass biscuit) refers to the cheapest, skankist white prostitute you can find.
I can't believe you fucked that ass biscuit. OR Dude, I saw your ex last night at the bar, what an ass biscuit!!
While our lifespan is the number of years we will live, our healthspan is the number of healthy years we will have and our sexspan is is the number of years we will continue to be healthy enough to continue having an active sex life.