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 just flip it immediately and stun them into silence
"I know, you can't even kill landlords anymore. Political correctness gone mad"
(as much as this sounds like a "and then everyone clapped and the lecturer was Albert Einstein" scenario, I said this out loud at a pub and got at least 5
reactions. At least some of my friends laughed)
I believe you.
I haven't tried that myself, but considering how bootlicky a lot of people are where I live, I can easily imagine them stunned by something said that was that far to the left of free college and legal weed.
When we had office debates / arguments about the government wanting to digitally spy on all citizens. The chuds that think “terrorists bad, so government spying good” always used to make the “nothing to hide? Nothing to fear” argument. I’d always do like you said and play along. “Yeah dude, anyway pass me your phone?” “Why?” “I want to read your texts and go through your photos” “Fuck off” “What’s the matter? Nothing to hide? Nothing to fear”. They never made that argument again.