What does it mean for a man who usually tells jokes not to joke in front of you?

First, I know you very well, so there is nothing to talk about. Second, he sees through you and doesn't want to talk to you. Third, he is in a bad mood recently and doesn't want to joke. Fourth, maybe he has other worries recently and is not in the mood for jokes. Fifth, I started joking, and slowly found that joking can't last long for everyone.