In my youth, I was one of those annoying people who corrected everyone's grammar, usage and spelling without even thinking about it. Now I'm old, I'm tired, and I screw up so often myself that I rarely say anything or even really care much anymore, but there are a few things that still make me crazy inside.
Typing "your" when you mean "you're". Or being too lazy for even that, and just typing "ur". Unless you are a lolcat, it makes you look stupid.
Saying "differnt" when you mean "different".
Saying "artesian" when you mean "artisan".
My brother will repeatedly say the non-word "sublantics" when he's losing an argument, whether it has anything to do with
semantics or not.
"Hun". I just hate it, I don't know why.
Speaking in baby talk to adults. My mother insists on calling things "gwooten fwee" instead of "gluten free". I have no idea why, as neither of us even used those words in a sentence until I was 33 years old and diagnosed with "ceweeac" (celiac) disease, and she is not in any way related to Elmer Fudd.
Any variation of the word "poop" or "poo". If you are over the age of five, and you still need to discuss it, you need to stop pretending you're cute- cute people don't talk about excrement in the first place, so just use the actual words instead of the baby talk.
There's more, but I'm probably starting to sound pretty pedantic (and I'm not, I swear!) so I'll quit before I alienate everyone here. I do realize I have plenty of annoying affectations myself, so thankyou (<----that's one of them) for putting up with me so patiently.