I'm a C for sure, but I'll be careful not to sing too loud if someone is standing really clause to me.
I don't get the people who don't want to hear the others sing... I think that it's the whole point of a show, everybody singing together! That's one of the reasons I like GA so much, because people around you know all the words and are so into it. I actually enjoy sometimes when the crowd is louder than the band... I even prefer audience bootlegs rather than soundboard ones because you hear the crowd better. If I only want to hear the band without background noise I can listen to the albums.
Now I have been stuck next to people who sang really badly and loudly the whole show, and it was a bit annoying, but I don't care that much because they were so into it. When you sing along the concert is an interactive experience, and becomes more intense IMO.
Anyways, I am from Montreal, and Bono told us during Elevation we were the loudest crowd of the whole tour! (it was also confirmed by Willie in his diary)So if you don't want a singing crowd don't see U2 here...