I think I'm in the majority, that it's mainly young people in cars, with the windows down, just loitering and playing some horrible techno thing, with the bass up so high that all you can hear is rumbling and the car is visibly vibrating.
Secondly, groups of chavs on buses showing off their new ringtones thru their crappy mobile phone speakers. This mainly doesn't happen from metal fans, because we have respect for our choice of music and understand it needs a good player to sound right.
I'm also against excessive swearing in public, sure, occasionally you might get hurt or be seriously angered by something and let out a swift 'oh fuck', but when you're trapped on a bus journey with a group of people who use profanity like other people use punctuation, well, it gets old real fast.