Animephiles. Oh goodness, they were horrible! Also, people who have no sense of shame and shout shameless things or just say them to loud, i.e., singing some kind of internet meme song in school or the middle of class or something, or making a vague reference in hopes that 1 person across the room will get it. Also, myself. I am a fairly annoying person, and am trying to work on that(successfully to an extent), but I always reflect on how stupid and annoying I was the year and years before. There was a pretty big change in my standard of living last year, as well as parenting, so I eventually realized that I was a huge asshole in many ways without even realizing it myself and that I wish I could punch my past self in the face, granted, I wasn't actually an asshole, and was still pretty nice, but I am now over-emphasizing every negative detail about me.
Also, people who insist on incorrectly correcting you, and parents who believe that often even a proper rebuttal or that voicing your disagreement with them or proving them wrong on any level is disrespectful and I find myself in opposition to my parents with somewhat regularity.