Decim has such a deadpan face all the time that he actually has to explain when he is joking. Also, he is not very good at telling compliments (said the Black Haired Woman's sandwich made for him was "terribly delicious").
Case in point, Episode 3. Childhood Friends Mai and Shigeru just get through having a heartwarming reconciliation. They accept their fate, but ask Decim for permission to have a final date before he sentences his final judgement. And then the Letting the Air out of the Band goes into effect with Decim says he's only willing to give them 5 minutes. It's only after his assistant starts angrily strangling him for killing the moment that he admits that he was kidding.
Episode 6. Just. Episode 6. Mayu is just a barrel of laughs. Her nonchalant response to most of what she encounters and Ginti's subsequent bafflement is hilarious.
The Black Haired Woman and Decim's unenthusiastic 'Yay' during the impromptu concert at the end of the episode. Clavis' excited 'Yay!' and pose are also funny. Ginti's expression takes the cake though.
BRADIO, the group that sings the opening theme Flyers, did a live-action version of the opening theme as a joke. The result can only be described as hilarious.
Even more funny when you see who plays Nona on that version: the clown.
Decim first attempt at smiling - well, it didn't go well. But he learns fast!
In the drama CD, Decim, the Black Haired Woman, Clavis, Nona, Mayu, and Ginti have the memories of music sent to them. They spend the drama dancing and playing games like the show's opening.
Decim quotes "Flyers" and says "puccho henzu eppu" (put your hands up).
can only be described as hilarious.