Judging a book by its cover?

I was on my way back from the faculty. Since I’m alone, I decided to move a little bit faster and rebut2 to squeez myself into the bus. I hate to be seen alone. No offence, but being alone is not cool ok. Well, I sat beside this guy, and he looked extremely skema; yes, the typical portrayal of nerd-do nothing else but study-anti social person you see in school. FYI, most of the bus drivers love to listen to Sinar.fm regardless of how old mature or young they are. So happens that suddenly the Guns n Roses’ Sweet Child of Mine was aired, and he started singing. I find it amusing that this guy had a very high ambiguity tolerance and definitely thin ego-boundary because he sung like no one else was there. Not to forget, the head-banging and leg movements at the chorus; which looked funny at first (oh, I purposely pinch my nose and try as much as I can, not to laugh. And succeeded! Ha ha ha). And his voice was, hmm, okay not that bad. To think about it, I believe most people tend to have this stereotypical thinking; or I’d say rigid first impression towards people we meet the first time. But I don’t know. Should or should not a book be judged by its cover? Or maybe what that guy did is normal, and I should anticipate that to come out from a nerd-looking guy? Anyhoo, I think you rock, Mr.! :)