It means the same as the phrases, "you bet your ass" and, "you bet your dick and balls".
That is, you're absolutely, positively, 100% certain about the final outcome of a situation.
{Seen on a website about flashlights, LEDs, and lasers}:
I tried to cut through the outer casing to bare metal with the blade of a Swiss army knife, and with some minor difficulty, I was able to do so. This shows the unit has a Type II anodized finish to it (...)
Would I really cut up a brand spanken new $450.00 laser? You bet your sweet patootie I would, if it's in the name of science.
A female who frequently has sex on the first date or first encounter.
Britney: Hey Lohan, did you call that guy we met at the coffee house yesterday?
Lohan: Yes, we met for drinks and well sex this morning.
Britney (laughing): Sometimes you can be such a back seat betty.
Nicole: Paris, did that guy give you a ride home from the club last night?
Paris(smiling): Yes, you could say that he gave me a ride last night.
Nicole: Your family should have been in the automobile business, because you are such a back seat betty.