Al Green sung the National Anthem at the NBA all star game in 2000. That was incredible. It's the only time I've heard the Star Spangled Banner at a sporting event and enjoyed it.

I would say people who try to invent new rythms in a song (never works). Solo's that are out of context and completely off the melody (though they can be cool in a rock and roll context). Whistlers who can't carry a tune, stay in any key, or keep any kind of rythm, it's the most hidious sound! I could also go on about things guitarists do that bug me, put I'm not sure I could remember all of them. Perhaps I'll try later