Bad Hygiene
Low Vocabulary and redundant use of words
Bias
Lack of structure or ambition (in general)
Lack of understanding
Lack of awareness and concern (especially of other people)
Lack of common courtesy and respect
Lack of appreciation
Lack of intelligence
Lack of experience (in certain areas which usually means they are one of the above if not more)
Lack of confidence (in general), will power, and courage
Lack of excitement
Self-importance
Lack of straight, thought out, standards of morals and ethics.
Lack of spine (confidence/courage/morals)
LIARS
That's about it. If you dig deeper into each one of those you get more of what annoys me. Just so you know, even with all of that I have managed to find someone and she is gorgeous, which doesn't hurt. ;P
This isn't only for turn-offs though, I won't conceder you a true friend if you're most of the above. Confucius has said "Never contract friendship with a man that is not better than thyself". That's pretty much what I go by. So my last and most important one is obviously:
IF YOU'RE NOT A FRIEND