The chunky, seemingly lovable Hangover II star was was in such a foul mood at the afterparty for the New York premiere on Monday night, puzzled partygoers were wondering who or what could have set him off.
And while his costars and director were rocking suits at the bash, at the Standard Hotel in the Meatpacking District, Galifianakis sported a scruffy full beard, baseball hat pulled down low and big headphones.
When two (really hot) girls aproached the star for a picture in the downstairs lounge, he scowled, shook his head no and walked past, mumbling something.
Then he disappeared.
So when did he resurface?
Not until late last night, when something, or someone, eventually persuaded Galifianakis to join the festivities. But the Between Two Ferns host quickly found a seat by his cohorts and stayed there for most of the night.
One insider at the party said Galifianakis had been "overwhelmed" by all the pictures and hoopla surrounding the event and needed a small break to gather himself. The actor had also skipped an earlier screening of the movie.
Cooper had a pretty brunette by his side for most of the evening. He was also joined by his old pal, James Lipton, host of Inside the Actors Studio, where Cooper long ago attended classes.
Galifianakis eventually opened up though, sipping white wine, shaking hands with fans and laughing with Cooper.
"He's great, I think he just got annoyed with all the activity," said the party insider. "He's here now. He's fine."