I use tho as short for though, and sometimes I accidentally type thou and forget the -gh (note: tho sounds like thoh as does though, but thou sounds like “thow”). That being said, unless my sentence is supposed to end with though (e.g. I get cut off), I don’t use it at the end of a sentence that it has no place in.
One big thing that irks me is when people use a word in a very wrong context. Widespread epidemic for example when referring to a supposedly popular slang term.
Anyway, what irks me the most (and typically after saying something else of equal stupidity) is yolo, y’all, rilly (which is what people say and write instead of RE ALL EE (really)), 'murica/'murca, anyways, like, y’know/ya know, and quite a lot of other stupid or entirely incorrect or contextually inappropriate terms, phrases, or word sandwiching.