From Sek Sau's portrayal of the Mo Yung F'uk character in DGSD '81, I've come to the following conclusion about the character: Mo Yung F'uk has no sense of humor at all.
The man neither makes nor laughs at jokes. People seem to be afraid to joke in his presence. All kinds of hilarious things could happen around this guy and he'd still be a stone face.
I don't think Mo Yung F'uk has a humorous bone in his body, not even in his elbows.