"First, kill all the lawyers".
The concept of metagaming is that each game is supposed to be played in on its own merits, trying, AS MUCH AS POSSIBLE, to ignore past results, alliances, and actions. Admittedly, one cannot ignore whether a person proved trustworthy in the past. However, there is a world of difference between thinking inside your head that you may not trust this person, and declaring that if you are ever in a game with them, you will attempt to kill them regardless of the circumstances.
Does this mean I think this person should be banned from playing? No. Is this person declaring in advance that he is totally incapable of reviewing each game and alliance on its own merits. Hell yes. And that's metagaming, counselor, regardless of the legalistic viewpoint.