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!"
2. 1. Testicles; those spherical spunk factories on the Scrots Road Industrial Estate. n. Courage; guts. As in "I like him. He's got balls". 3. exclam. Denial. As in "Has he balls got balls!" 4. n. Rubbish; nonsense. As in "Balls! Of course he's got balls". 5. n. Round things you play football with.