If I add someone to my banlist...

[swsnowman]

If I add someone to my banlist and join a MM game...will it prevent them from being on the same team? or atleast NOT in the game?

[Dgenerate`]

If you add someone to your banlist, you actually exclude them in real life too.

[Okuu]

No it won't.
I suggest that you use the RAP feature at the end of a game whenever you see a comportement that you judge not acceptable