I've rewatched the whole series three times now and I'm convinced Dean's humor is basically a trauma response wrapped in a leather jacket. The one-liners aren't just jokes—they're pressure valves. When he's about to face down some ancient horror and cracks, 'Rise and shine, Sammy!' it's not just to lighten the mood. It's a way to maintain control when the world's gone sideways, to remind himself he's still the big brother who can make his kid brother roll his eyes even in the apocalypse. His default is sarcasm, but the delivery changes depending on who he's talking to. With Sam, it's fond exasperation. With Cas, it's bewildered affection masked as annoyance. With Crowley or some random monster, it's pure, sharp defiance.
That's why the quotes that stick with me aren't the overtly funny ones, but the dry, grim observations. 'We're all gonna die. I'd rather go out like a man than wait around for it to happen.' It's bleak, yeah, but the humor is in the sheer, absurd stubbornness of it. He's not laughing because things are good; he's laughing because if he doesn't, he might start screaming and never stop. The humor is the character, not an add-on. It's how he translates love, fear, and loyalty into something he can actually say out loud without choking up.