I like efficiency, so pretty much anything that slows me down is a pet peeve:
slow walkers on the sidewalk, or groups that aren't paying attention, and are just meandering around
On an escalator, anyone that doesn't obey the "stand to the right, walk to the left". I have very irrational anger over this. I fantasize about just shoving people sometimes. I need help.
On a train or bus or elevator, people who stand at the doorway instead of moving in. I fantasize about shoving people here, too. I think I need to go to more yoga.
When driving, cars that basically swerve to the right in order to take a left turn, blocking as much traffic as possible. Really, anyone blocking my lane is a pet peeve.
Aside from efficiency-related things, I have a major pet peeve about people not trying things. People who say they "don't like apples", for example, but haven't eaten an apple since they were 3 years old 40 years ago. Or say they don't like something that they've never tried is even worse. You've never tried it! You can't "not like it"!