Depends on the situation.
At dinner in a resturaunt, probably not.
during sex, depends on what you're into
it's funny as f***
I always go "holy crap what's wrong with my belt loop, can you take a look since it's way in back?"
Then I try to wait until they get close and their mouth is open before letting one rip. Works every time.
Then, introduce yourself and offer to buy her a drink.
Farting during sex is a fantastic excuse to abuse her "sloppy fanny".
Not only is it ok, but I recommend it. That's how I got my lady.