Despite the title, this is, in fact, a comedy trope. Because there is something funny about watching someone attempting to be funny and failing. To be funny, that is. It's just funny. Got it? This is essentially a character who screws up any attempt to tell a joke. Perhaps they forget the punchline, perhaps they have no sense of timing, perhaps they try to explain it until it stops being funny. Whatever the case, any attempt to make a joke will leave their intended audience staring at them dumbfounded. (Or possibly laughing, but not for the intended reason, if the intended audience enjoys Anti-Humor, which this often bears unintentional resemblance to.)