People who feel the need to write in a very obnoxious font. This includes cutesy fonts that are barely legible and neon colors like this. Why? Just why?????? If it's a profile or some form of advertisement for yourself, that's fine. Annoying, but understandable. You want to physically stand out. But on a medium (like a public forum), there is no need. And the sad thing is that sometimes the poster writes extremely well-worded and intelligent responses, but it's so obnoxious to view that most people won't even read it. Take my advice: use that Super Special Font and use it in your profile and signatures only. Type your responses in the normal font.
Also, people who use #hashtags everywhere. If you want to be found via searches for #[description of yourself] via Twitter or Instagram, cool. But if hashtags are not used on other media, they shouldn't be used. Of course, you can do it as a "tongue-in-cheek" sort of witty thing to emphasize a point, but if they are not used on that medium, then they're pointless. Reminds me of this scene from Mean Girls:
Side note: I now take over this thread as "Daily Annoyances." Carry on.