Of course there are the trolls/ones who ignore commands, etc. Here’s a few off the top of my head.
Controlling ground, requests to change frequency by pilots wanting to switch to tower for takeoff clearance. Not a big deal, but if you’re busy controlling tower and ground, it can be especially annoying.
Misuse/misunderstanding “transition” and “go around”
Not taking off in a timely manner after being given clearance.
Repeated requests for takeoff when there are multiple inbounds for landing and no room to fit you in. Dude, be patient.
Stopping on the runway after landing and requesting a frequency change.
Poor understanding of sequencing and cutting in line of the pattern.
Lining up on the runway before being given clearance
The biggest thing I see while scouting on TS is the controllers from miles away sending me an on guard message even though I am at another airport. The same is true at the same airport where two different people are on tower and ground. Tower should not be sending me a message while parked at the gate and me logged into ground.
This is a big problem especially at KPSP, the pilots usually are too lazy to taxi to 31L when I tell them to, then they taxi to 31R which is often way too small for the aircraft. Then when I tell them to taxi to 31L, they just ignore it and takeoff.
When pilots don’t understand “make a right/left 360 for spacing”, “go around, make right/left traffic”, “turn base”, “enter left/right downwind”, “line up and wait” (that does NOT mean hold short and it also does NOT mean taking off), and of course the one grade 1 noob that thinks he can file his flight plan whilst ON the runway after being “cleared for immediate takeoff”.
Don’t forget that it’s not always the pilot, ATC can be bad too…