1) All of the photos on social media sites where the people have their arms extended way out in front of them to (I assume) hold their cell phones to take photos of themselves. I see very few photos of people with their arms in normal positions anymore.
2) Social media photos of people making funny faces and holding up their fingers, as though that were a particularly clever thing to do for the camera.
3) Social media photos [Sensing a theme here??] of people taking photos of themselves in their bathroom mirrors, especially when you can see other parts of their bathrooms in the background.
4) Social media photos [yes, it is indeed a theme] of people where their faces are distorted because they are holding up their cell phones right next to their faces to get close-up shots.
5) Over-sharpened and over-saturated photos (anywhere, any time).
6) Rude and arrogant remarks on [photography] forums.
7) Answering questions that specify certain parameters with a recommendation that does not fit those parameters, or criticizing the OP for even having parameters.
8) People who post on [photography] forums with "I haven't read the entire thread, but. . ." and then post something that someone else has already posted.
Edit: And yes, I realize that some of my pet peeves are the same as some that have already been posted. Nonetheless, I have read the other posts and they are still my pet peeves, also!