I hate all bad grammar and punctuation and spelling. Not only am I studying English at uni, but I also read things as they're written and my brain absorbs it literally. The minute someone messes up grammar I have to take time to stop and figure out what they meant, which sometimes only takes a second or two, but more often takes longer because most people mess it up so bad. I know I'm not perfect at this stuff myself, but some things are really easy to do and people won't do it.
I really hate when people don't capitalize or appropriately identify the names of songs, books, movies, etc., when they're talking about it. I don't mind if you don't know which ones require quotation marks and which ones should be italicized but at least differentiate the title from the rest of the sentence. For example, sometimes movies or books or shows have a name that doesn't imply it's a title immediately, for my example, let's say there's a new movie out called "The Game." People like to make posts like this, "hey guys lol im at the game so awesome" When you read something like that, it could imply a lot of things, it could imply a ball game, or a video game tournament, or any number of other things, and all you had to do was capitalize the words to make it more obvious, and it doesn't take that long to push the "Shift" key while pushing a letter down.
Mistakes like those are especially frustrating because if you comment on it these idiots will act like you're an idiot, and do it with their bad grammar. I don't expect everyone to be perfect but can't people at least try?
I also hate many of the ones mentioned here already and I absolutely destest people who say "are" instead of "our." :okiedokielokie: