Trolls.
Trolls piss me off, and I know what you're thinking, "Well of course trolls piss you off, THEY'RE TROLLS! THAT'S WHAT THEY DO!" And yeah, you're right, but it doesn't change the fact that they are annoying, exist for the sole purpose of making everyone's internet experiences worse and more toxic, and sometimes cause serious problems.
For example, how many of you have heard that cultural appropriation includes things like eating sushi, wearing jeans, and learning other languages? Well, here's the thing, it doesn't, those things are not now, nor have they EVER been included as forms of cultural appropriation by ANY serious Anthropological or social study on the subject (and yes, cultural appropriation IS an actual Anthropological concept, it was not invented by Tumblr, Google it), and anyone who's done their research on the subject will know that. The reason people sometimes think they are is because those ideas were spread around by trolls in an attempt to make so-called "SJWs" look bad, and as a result we have a group of misinformed people on Tumblr who found those troll posts and believed them, a group of misinformed people on Reddit who found those troll posts and use them as evidence that "SJWs HAVE GONE TOO FAR!" and we have a group of people desperately trying to un-do the damage that these trolls have done.
Not only that but they've made surfing social media a toxic chore, made online gaming a terrible experience, and become the absolute bane of anyone who wants to talk about something seriously on a forum (to the point where my very use of the term "cultural appropriation" may upset some people even though it's not my intent in doing so, due to just how bad an image the concept's been given by trolls).
I know I shouldn't let trolls get to me, that's what they're after in the first place, but as someone who's always had a little bit of difficulty telling apart sarcasm from earnesty, trolls make my internet experience significantly worse than it otherwise would be.