In the first couple of seasons, Malcolm seems (in general) to be pretty friendly and, apart from his genius IQ, he's normal. I can't really comment on how he is in later seasons, because I haven't seen much of them, but he seems like a guy who could have a good group of friends.

But then again, in the first episode, Malcolm complains about people at school thinking he's weird, so maybe he was never too popular even then. I wonder why exactly they thought he was weird? Was it perhaps that they noticed he was doing much better work than them?