I think people crack jokes when they genuinely think something is funny. At least I do. I get on my hubby's nerves because I crack jokes and laugh at them even though he doesn't think they are funny. I'm not selfish and I'm not immature. I usually crack the most obnoxious/stupid jokes when I'm hypomanic, no other times.

I don't crack jokes in serious situations, however. It sounds like the person you're referring to doesn't know when it's appropriate. So I don't think joke-cracking is bad, it's just knowing when it's appropriate and stopping when it's not appreciated.

Is there a way you could talk to this person about it gently, e.g. saying "I appreciate that you find humor in so many situations, but I don't think it's appropriate to crack a joke in such-and-such situation." I would use a specific situation. Don't generalize by saying he does it ALL the time, because then he will feel attacked like you don't appreciate him or like him. Just a thought.