I don't propose this as a end-all solution to rudeness in the Coliseum, but at the very least it will reward good players while allowing a reasonable punishment of badly behaved players. It is by no means foolproof, so if you find a flaw that you can fix, please DO post a response!
1. At the end of a match, you may give any player on the opposing team a +1 or -1 for their conduct.
2. HOWEVER: if that player did not speak in Public Chat (pre-game locker room, during game, or post-game) negative ratings are not recorded.
3. Player ratings are reduced by half (at the same time Coliseum records roll over), whether positive or negative.
4. Players with at least 20 ratings and more than 2/3 of them good (twice as many people enjoyed playing with you than disliked playing with you) gain a green honorific indicator; more than 3/4 or 4/5 could also have their own cosmetic perks.
5. The same would be applied to negative rated players using red, but with the caveat that at the second level, any green-rated player can kick you, and at the third or higher level, any neutral rated player with 20+ ratings may kick you. Parties with a kick are returned to Haven and placed at the top of the LD queue.
6. GvG games are not rated.
Before people say this is open to abuse, let me make a few statements:
-If you keep your mouth shut, you can NEVER be rated negatively. Thus, if you can control your temper, you can NEVER fall into the red.
-The system is relatively foolproof against gaming, as you cannot create closed GvG rating-booster games; if you can get sufficient friends to rate you, then it's not really gaming since they are your friends and actually enjoy playing with you. (Besides, they actually have to play through to the end of the match)
-The system avoids punishing newbies and infrequent Coliseum-goers by a) requiring at least a certain number of ratings total and b) decaying the ratings at the end of each week.
-The latter also allows ANY red player who has a change of heart to recover their reputation by simply not speaking in games.
Kicking players, crippling the enemy team just beacuse they are bad mouthed isnt good.
It can be abused in that sense.
Just /ignore or disable their chat.