Classic Japanese comedy...
...(think three stooges Moe vs. Curly only a bit less violent) has ritualized roles. Friends can sometimes slip into one of these roles for the fun of it. If one begins a gag and the other does not play along there's a problem. The one who refuses to play along gravely insults the one who started it. He implies that the one who started the comedy was not doing comedy at all - that he's really a stooge.
So thanks for that.