Unintelligent, narrow minded and thinking they win the conversation with 'Naaa naaaa you're chatting bullsh*t', generally acting like the dogs bollocks and making fun of other people all the time, and if they haven't washed.
If he's overweight or if he's constantly being loud or making fun of people.
Low self-esteem. If he's not confident in himself why would anybody else be confident in him. I'm a shy person but I don't have low self esteem and I'm confident in myself and what I can do. I may not always be the most confident when talking to other people but I know what I can do and I don't care if anyone else sees that or not.