Thanks for the request, @biz! I've made a similar list before (THINGS THAT FREAK ME OUT) and a lot of those things would also qualify for this list. However, since 'uncomfortable' sometimes feels like my default setting, I have a couple more to add.
  1. When someone I thought I knew well and liked, turns out to be sexist, racist, homophobic, etc.
    Such a bummer.
  2. Talking about sex-related things with my parents.
    Or even just hearing them talk about it. This doesn't happen often though, thank god.
  3. Ted Cruz' face.
    There's something disturbingly wrong with it.
  4. Pro-life/anti-abortion people.
    I'm sorry, but there something very wrong with you if you do not support a woman's right to choose and to have proper access to clinics. It's perfectly understandable and respectable if you wouldn't want to have an abortion yourself, but do not deny others the option or judge them for having one. Actually, I'm not sorry. Fuck you.
  5. Talking to someone who aggressively clings to the right-wing fearmongering demagoguery perpetuated by people like Donald Trump, or the asshat I mentioned in my third bullet point.
  6. Public bathroom stalls in America.
    Does privacy mean nothing to you? Why are the doors up so high, and yet so low? Why is there a huge space between the door and the wall? This makes no sense to me.
  7. Life.
    Yikes, am I right?
  8. Being someone who doesn't know what he's doing in a room full of people who do.
    Like at a networking event (I'm stealing that one from @ltoiaivao ).
  9. The continuing popularity and success of The Big Bang Theory.
    Stop it.
  10. Aggressive masculinity.
    Stop it.
  11. People who post way too detailed updates about their health, their kids, or Minions on Facebook.
    Stop it.
  12. Guys with the incessant need to remind people that they're actually nice guys who deserves to have girlfriend, and believe that the friend zone is a real thing.
    If you constantly have to bring up how nice of a guy you are, that's not a good sign. You're blind to your terribleness. (Inspired by @RachelP )
  13. The power of corporate lobbyists in politics.
  14. My parents (and especially my mom) talking bringing up something I don't really want to talk to someone else, and then forcing me to talk about it to that person by setting me up to do so.
    Especially when it's about medical stuff or something about my love life that I'm not really ready to share yet.
  15. People who get upset when a fictional character is played by someone of a different ethnicity or gender than they're used to.
    And by people, I obviously mean white people getting upset when a character they're used to being white is played by a person of color. The reverese is absolutely valid though, whitewashing is a problem. And a good example of the genderswap thing is the upcoming Ghostbusters movie with an all female cast. People who get upset by that make me sad and uncomfortable.
  16. Men who idolize Dan Bilzarian.
    Gross. Stop.
  17. 'Fans' of pop stars who send death threats to people who make fun of their idols.
  18. Science deniers, and especially ones with political power.
    Scientifically proven to be fucking idiots. Dangerous fucking idiots.
  19. People invading my personal space, or watching them doing it to someone else.
    To quote The Police: "Don't stand so close to me."
  20. People I don't know (very well) who insist on touching me when we talk.
    Why? No. Stop. Having your hand on my arm, shoulder, back, or anywhere else does not improve this conversation. Step back please.
  21. People who aggressively defend outdated and offensive traditions.
    You are on the wrong side of history. Stop it.
  22. Gratuitous rape scenes in movies and tv shows.
    I'm talking to you, Game of Thrones. These serve no purpose. Make it stop, assholes.
  23. Wet toilet seats in public restrooms.
    Why is it wet? How did that even happen? What kind of monster doesn't clean it when that happens?
  24. Corporations trying to use memes on their social media channels.
    Stop ruining things people like! 99 times out of 100, this is more painful to watch than anything else.
  25. People who insist you call them by a ridiculous self-appointed nickname.
    No, I will not call you T-Bone.
  26. People who invite themselves to visit or tag along, especially when they just show up unannounced.
    It's rude. Either ask in advance, or let me invite you.
  27. When someone says "guns don't kill people, people kill people," and mean it.
    And then saying that having more guns makes people safer. Get your head out of your ass.