In real life? Eh, pretty neutral.
In stories, they’re handy because, as a trigger, they can push a lot of different buttons. Obviously there’s the smell of them, which works for “raunch/musk”, but the uncontrollably of them can give imply a certain “loss of control/incontinence” without having to get into anything messy. In addition to that, the act of farting implies either crudity (if the person enjoys/flaunts it) which supports a “redneck/lout TF” or they can be embarrassing, which triggers “Humiliation.” They’re just versatile more than anything.