When it's a constant wall of noise rather than a rare occurrence (because let's be honest, how many conversations have you been part of that assume everyone involved thinks/knows Trump is a joke? How many comedians, articles, TV shows, monologues, etc?), the effect on people can add up.
At this point I'm 100% sure that everyone with a mental age of 12+ years knows that Trump is a joke, but alarmingly many of them still think that he's a
funny one. "Never mind that he's a liar and a scoundrel – he's still 'one of us,' right? He'll show those damn liberals what's for, and that's more important than actual political outcomes, no doubt about that."
They feel that they are the 'social out-group' you talked about. And perhaps they have a point - would you feel comfortable telling your friends and co-workers you were going to vote for Trump?
If I were a member of the Trump-loving Red Tribe, I would feel 100% comfortable informing my Red-Tribe friends and co-workers about my choice of candidate – after all, they'd be voting for him as well. As for my Trump-hating Blue-Tribe "friends" and co-workers... well, I'd probably tell them who I'm voting for without telling them
why, and I'd do it as confrontationally as possible, with accusations of "elitism" thrown in. My Blue-Tribe "friends" and co-workers would undoubtedly respond with accusations of sexism and racism, in a tone that clearly confirms my expectations of Blue-Tribe condescension towards my tribe: "Those out-group bastards
refuse to tolerate my in-group – I'll fucking show them! Even if Trump turns out to be a gay Muslim pedo-rapist-murderer, I'm still voting for him just to spite those condescending out-group assholes!"
None of this would mean that the out-group is necessarily
wrong about Trump being a terrible candidate, but who cares? Politics is no more about politics, just entertainment and social signalling.
EDIT:
Why the fuck am I sitting here on the dole when I could be making megabucks in research grants WITH REAL STRONK FAST GRANT TRUMP MAGIC?