Mainly any sort of "censorship" bullshit. Off the top of my head, the stuff surrounding Star Ocean 5 and Overwatch were particularly embarrassing, as were much of the Nintendo controversies. Claiming inclusion of women/non-white ethnicities is "SJW pandering" is also a good one.
"Sakurai made Melee great on accident and Brawl bad on purpose" is also particularly teeth-gnashing for me; actually, for whatever reason, Smash Bros. is host to a lot of weird conspiracy theories (a phenomenon even
Sakurai has noted) and I'm still trying to figure out why. While I'm at it, certain complaints regarding Smash 4 have always struck me as either being hyperbolic (stage design) or downright head-scratching (Wii U's Classic Mode). Consequently, I always feel alone in enjoying them.
Also, not sure if this counts, but I've found discussions surrounding Mario 3D World and Skyward Sword get so overly defensive I can no longer participate in relevant threads for my own sanity.