i was just playing grim fandango for the thoulsand time and i got curious

DID ANYONE EVER FIND OUT WHAT THE HECK DID MANNY DO AT CHRISTMAS????????????? its been driving me crazy just like guybrush's porcelein phobia

Manny was drunked.... But I can't remember what he has done... Something wrong I think...

I'm pretty sure he punched Dom after getting blitzed.

Then he got thrashed. If he was so drunk he couldn't remember, Domino probably only had to push him over.

He probably punched Domino:

Manny: "I want to punch you in the mouth."
Domino: "Oh, not the Christmas party all over again."

There's no way to really know what happened at the party. There are a few pieces of dialog that give a general idea of what happened.

Manny -- So... you going to the Christmas party?
Eva -- After the spectacle you made of yourself last year? I wouldn't miss it for the world!

Manny -- I wanna punch you in the mouth.
Domino -- Oh, no. Not the Christmas party all over again.
Manny -- What happened at the Christmas party?
Domino -- Blacked out on the whole thing, huh? Maybe you should switch to lemonade, kid.

Domino -- At least at the Christmas party you passed out before you really got hurt!

My guess is that Manny got very drunk, got angrier at Domino the drunker he got, started to pick a fight, and then passed out before anything serious happened.

how bout this

Manny gets drunk then angry at Domino, tries to hit him in the mouth, misses, goes spinning around the whole room making a spectacle, hits his head and blacks out