It really is terrible at humor. I tried asking ChatGPT some dumb joke questions like "if I melt dry ice, can I swim without getting wet?" Any human being would know that this isn't a serious question and is intended as a joke. But ChatGPT gave me a short lecture on the actual chemistry of dry ice and then clarified how dangerous it would be to swim in or with dry ice. The joke went way over its head.

I asked some other similar questions. ChatGPT has zero sense of humor.