For me the easiest tell is the up front, unprompted, and unsolicited declaration of nonpoliticalness. When someone takes the time and expends the breath to announce how nonpolitical they are, what follows is almost always a rant about how everything/everyone else is too political these days, and that of course leads into something between status quo advocacy and outright reactionary/regressive sentiments for some fabled time before those wicked politics were visible to the nonpolitical ranter. 
People that are hostile to service workers. Some just want to take some ideological stand against tipping when the service worker doesn't really have a choice and needs those tips to survive in the current unjust system in a way where ideological purity gestures toward that service worker just look like being a greedy and sanctimonious asshole. The worst of such people will actually declare, shamelessly, that they believe that service workers don't deserve a living wage. The implications of that are 
worthy.
I may get shit for this, but I'll say it anyway: this hair and beard combo, seen on living people. 
I have yet to meet anyone in person with that look that wasn't a chud.
(If one of you is a comrade with that look, I am sorry in advance for the prejudice and if I ever meet you in person I will atone by buying you a drink or something.)
I approach it the other way. Just assume most people have absolutely awful political opinions. Pray they don’t believe all homeless people should be thrown into internet camps and gassed. And then if I find out they don’t believe that I bring light into a somewhat correct political leaning and then try and crack it open. Often I use landlords as the go to bad people and see if they agree r if they seem confused why I hate landlords so much then I go into detail.
Ah, the old game-and-gas routine
Oh God please don't send me to hexbear
Sorry about the gas. We had refried beans last night.
You'll be fine just stay away from the owls