The best ones are the ones who are motivated and want to learn. I would rather teach a student who is less than gifted but puts in the effort to do what is asked of him/her rather than some hot shot who thinks he knows it all and never prepares what is asked of him/her. The other annoying ones are "my daddy is an airline pilot, and he says i have to be one too" (I am sure there are genuine airline pilot's sons/daughters around too).