I make jokes a lot. It's a defense mechanism. Their humor maybe isn't your cup of tea, or maybe you're just more "serious" than them. There are of course times best kept serious, but even then, sometimes a joke can break the ice. I have a lot of laughs with my girlfriend and we joke about some really unusual stuff; it's how we cope and it works for us. My humor isn't for everyone. I try to be particularly careful around strangers or of course in formal situations.