Leon is, well...resident asshole. XD I doubt he has anything in particular against Malachi....but I doubt they are friends, either. Just one of those things. Malachi might be among the group that could possibly remember Leon being a nicer guy, once upon a time.

Brain- Yeah, Brian would be a little "omg you are a senior" followed by "omg you are one of those evil, mean people" in his brain. Never allowed. He'd probably try to stay out of the way, because Brian is just like that.

Ginger- Probably knows him in a vague sense. Might have had a fling with him in the past? She's pretty much the 'anything to make me popular and people to like me' type, so...it is possible.