People who sing along at concerts

MMmmk.  I hate it when people sing along with the song being performed whether it's sitting in your living room watching American Idol or if you're actually at a concert.  I understand there are times at concerts where the artist asks you to sing along and that's fine and dandy but when you're in a room full of people who have gathered to listen to a person/band perform a song... they don't want to hear YOU sing.