Some people curse at a knee-jerk reaction and that's OK. As a habit, well that's annoying. I've had friends in college say the F word multiple times and it's quite sickening knowing that deep down inside and on the surface, they're just pansies trying to talk tough as if they were short on confidence and bravado.
I think it depends on place too. Personally, I don't swear often but at the pub watching the football (ahem, soccer) on the tube, you'd be a bit odd if you didn't call the ref a proper wank every now and then. You're having a beer, a heart-clogging English breakfast with like-minded individuals, why not let out a curse; it's guilt-free for 2 hours. My father is the same way. He never cursed unless the football was on, not during baseball, American football, basketball, or any other American sport. It had to do with the football. I was expected to follow suit.