gimil wrote:what if i put them on the list mid game?
No, don't think that works. Feedback is allowed if and only if you have completed a game together. Putting someone on your ignore-list mid-game I believe eliminates his postings from the game chat in your view. It has no effect on whether feedback is allowed or not.
Going forward, a person on your ignore-list will not be able to join a game in which you are a participant, so in the future there will be no new games that you two have completed together.
You and he could still leave each other feedback based on any earlier completed games, but only one feedback for each category (positive, neutral, and negative) will be allowed between any two players.
In most cases negative feedback is so poorly written that it's effect can be entirely negated by your response. Often negative feedback reflects worse on the writer than the recipient. I wouldn't worry too much about it. If it's truly unjustified or violates one of the guidelines you can petition wicked to have it removed.