1) Anything less than 3 chars really gets on my nerves. It really hurts readability, since 3 chars at least usually gives you at least one vowel. Personally, I try to use at least 5 chars.
2) One pet peeve I have is class names ending in class (ex: personClass or buttonClass) since it kind of takes away from the fact that you're making an object, not a class. Making instances of a class similarly I find ok (ex: blueButton, redLabel), since it's easier to read, but the class thing can get really annoying.
