I have always found that if you ignore obnoxious folks like that, they will either leave or act right, as others have said, a lot of times they do it for attention only.
I agree that many teens just want attention, so don't give them a reaction. Just go on you merry way and don't react. They won't find it "fun" after that and won't do it again, eventually they'll stop.
Teens love attention....best way to deal with it? React back in a way they don't expect. I had some kids yell out from a moving car as I was walking along..."Hey, wanna f...k?" I looked up and said, "Yes, please! Oh with you? Nah, no thanks." They giggled and turned red and shut up and did the window up. My mum said she had kids do the same thing to her and she replied...'You disgusting foul mouthed..." they then mooned her...See... they EXPECTED someone to react and it made them worse.
Yes, there are those that even like to give the illusion they are kind, Christian type folks but the truth is they are deplorable, intolerable human beings who have control issues beyond comprehension. They should be pitied too.
Trinity
Yes, some people are very mean and its hard to understand. But don't let them change who you are. Pity them. They need each other to feel big or strong but they are nothing but cowards really.