I seriously can't think of an occasion when I have seen a fan at the match boo a particular player. I remember the sarcastic cheer when Howard caught a ball last season (which i thought was stupid), and the groans when Stones was Cruyff turning in our own box, and obviously I've seen fans boo at the end of a game when we have looked like we haven't tried (I don't really agree with that either), although i'm pretty sure the boos at the end of the last game were aimed at the ref.
The Alex Nyarko confrontation is the only time i can remember a fan doing something where the player knew for a fact a fan was pissed off with him.
Fella by me at the Watford game last season booed Kone when he came on and got off straight away.
Awful behaviour.