I am part of a social board games group that meets most weekends to play short (max one session) games that usually involve role playing of some kind.
Recently someone invited a friend from another, more "serious" gaming group. Since then, all of our games have become so stilted. In particular, this person is heavily against "metagaming", and frequently stops the game to point out examples, makes us replay moves that shouldn't have been allowed, etc.
For example, player A prematurely attacks a monster that he wouldn't be able to defeat alone, making a joke that "Jim won't bear the thought of not getting xp from this kill, so he'll save me". Players deliberately play pranks on other people's characters when the player goes to the bathroom, even though technically their character is there and would stop it if the player were there. Real-life relationships are exploited even when not mirrored by the characters: "better give Sally your share of the loot or you'll be sleeping on the couch tonight!" And so on. We usually come up with flimsy excuses in-game for these actions, but they are transparently made for out-of-game reasons.
Since the new player joined, all of that has stopped. We are all a bit intimidated because they are a more "serious" gamer than most of us, and they gave such firm reasons for why metagaming was the worst thing that could happen in role-playing. Well, we tried it, and it completely ruined our dynamic. Other players don't want to come any more when the new player is coming. Is there anything we can do, or is disinviting this player the only option?