YOU WON'T DO A FOOKIN THING. At least I hope not. MLS exist to prey on your lesser nature, which includes blow-outs to further divide you from your friends. No MLS is worth losing a friend over, and they're counting on that. They count on you acting like the fool so they can tell your friends, "Look at this r-word right here."
Here's an easy phrase you can parrot.
Yes ... but you need to leave.
Say it low, slow, and clear. You don't need to say anything else.
"Yes ...." acknowledges their power, which is important to them. You need to make them feel powerful, because resolution NEEDS to be their decision (to do what you want). There are other ways of making the other person feel powerful and ready to make decisions. (This is the key emotion to negotiating: the other guy has to feel like he came up with the deal you wanted all along.)
The pause is important. Saying it low and slow is important, because all of that feels very much like a "lemme level with you" type secret, and we all love to be let in on a secret, even if it the secret is horseshit.
"... but you need to leave" is the gentlest brick wall. It firmly establishes a solution to a problem, and it's very unequivocal. There's no room for argument. It also spares you from having to think of anything else to say, and you want to focus your energies on grilling. They'll run out of excuses, because each one will be met with "You need to leave."