What is your spelling/grammar pet peeve? Anyone have the same as mine?

[Lauren]

Mine is when people say "on accident" instead of "by accident," because people say the phrase "on purpose" and think the same thing applies to "on accident." Also, I've heard many of my teachers make this error, so I guess the knowledge about this error isn't really well-known.
Also, I hate when people just automatically correct something like "my mom and me" to "my mom and I."
People don't realize that the "...and me" part is grammatically correct in many cases, but they don't use it at all.
Lastly, it annoys me how many people cannot spell the word "definitely!" I see the word "defiantly" so many times on social media because I guess AutoCorrect changes it, but I'd say you should still edit the tweet or post by yourself after it AutoCorrects. And then when people spell it out themselves, many get it wrong anyways. For example, I see "definatly" a lot, and many other errors with this word.

So what are your own pet peeves, and do we have any similar ones?