handshake thumbs up combo
Because they are all insecure on the inside, and no matter how big they are, they try to look even bigger every chance they can get. Notice in this pic, Kovacs went for the fist bump, but the novice/twink/schmoe on the left went with the thumbs up, as if to say "no way man, I'm doin the thumbs up, fist bump won't show my biceps from this angle." What a tool, check the fanny pack.