On the cringe-o-meter, "group of friends singing loudly in a fast food joint" merely rates as "irksome and mildly embarrassing" for me. It's not too overly different from sports fans getting hammered and singing "On Wisconsin" or "Fight Fiercely Harvard" or whatever sports fans sing.
The local furmeet was allegedly dis-invited from a local sit-down chain restaurant for just being too loud in general, and that actually makes me cringe more, even though I never went to that particular meet.
Re: that Mike Nelson screencap, I definitely cringe when people fight lulz with whining or soapboxing. The way to win over a comedian is usually to be funnier than them, NOT lecture them about how their joke triggered you. This goes for social justice warriors, too, as well as bronies and furries.
My brony friends are actually fine. One friend was initially overly-fixated on the ponies, but he's also on the spectrum, so. Otherwise, no cringeworthy conduct from them that I've noticed or heard about.
I have a couple of friends who pride themselves on being "edgy" and "politically incorrect," and they'll sometimes say inflammatory shit within earshot of my social justice-y friends. Cringe, flinch.
Also have a couple of friends who are just pedantic neckbeards, and I'll cringe when they trap someone in a corner and start lecturing about nerd shit in a Ben Steinian voice.