Saddlebacking - the term for the phenomenon of Christian teens engaging in unprotected anal sex in order to preserve their virginities. Named after Saddleback Churh, home of the Reverend Rick Warren, who is a proponent of abstinence education, the "sex ed" that has convinced so many Christian girls and boys that buttfucking isn't actually sex.
Saddlebacking - After attending the Purity Ball, Heather and Bill saddlebacked all night because she's saving herself for marriage.
The fresh mix of lube, blood and fecal matter that is the by-product of nubile Christians engaging in unprotected anal sex to preserve their virginity.
Sheesh! I have seen this phrase misused a few times now (even in Roger Mellie's Profanisaurus!). Let me clear things up:
Saddlebags is a word to describe the bulging areas of fat on the upper outer thighs of ladies, in a way that resembles saddle bags being carries on a horse.
The expression was used in Ace Ventura: Pet Detective. I can't remember exactly how though. It was something along the lines of:
Melissa Robinson claims she isn't fat. Ace says something along the lines of "yeh, whatever you say, saddlebags!"