Unfortunately, I've been in the situation of dis-inviting several people over the past few years--I've seen everything from terrible hygiene issues to playing WoW on the laptop at the table to blatant/creepy sexual advances. Even in groups where I'm not the GM, I usually get the task because I don't have a problem telling people the way it is.
When it gets to the point that a player is on the fence, I'll chat with that player (either in person or email, doesn't seem to matter). I'll ask questions about the undesirable behavior and ask why they did it--if they're being a jerk, they know it. The typical response is an apology, a mending of the ways, and the issue is never a problem again.
On the other hand... If they get defensive or jump into an obviously rehearsed diatribe (i.e., they either don't see a problem or have no intention to change the behavior), I'll bring the situation before the other players and we decide whether or not to keep them. Then it's as simple as, "Hey Bob, the group has talked about it and it's not cool. We're all here to have fun, but this behavior is unacceptable. We're not playing with you next week. Good luck finding a group that's a fit for you!"
To me, it's very important to phrase it so that it's clear that you are making a decision to not play with the offending party based on the behavior. Some people just have a disconnect between cause and effect. The five geek social fallacies are applicable here.