Colloquially, it refers to a bad player; however, this is not fully correct. A scrub is a player who places artificial rules on himself solely to limit his skill.
I don't understand how asking a couple of questions in order to improve oneself is a scrubby thing to do.
I was exaggerating on the number..
For instance, Mew2King can beat almost any Diddy Kong. Why does that mean he knows the match up? He's not that great at it, (Nor am I so I really shouldn't be one to talk, but whatever.) and he admits it himself.
So yeah. If MK is banned I'll pick someone else. I highly doubt this will happen though, I don't know about you. :S