Pattinson defends Ledger

No laughing matter!

According to a witness at the No on H8 show at The ­Improv in Hollywood on Dec. 16, Twilight star Robert Pattinson, 22, booed a comic who said, "Here's my impression of Heath Ledger," then collapsed and began faking convulsions.

(Ledger died of an accidental prescription drug overdose in January.)

"Robert and his friend went nuts yelling at him," the source tells Us Weekly. "[Pattinson screamed] f--k you! You suck!"

But the actor -- who recently cut his famous hair -- went unrecognized by the performing comic.
"The comic didn’t know who it was, but I'm sure he found out later!" the source tells Us.