Some of mine:
The imbecile who can’t be bothered to fly an extra downwind leg and decided to land against everyone else.
The total idiot who cuts you off on final, forcing you to do a 360 or go missed.
The disgrace to society that are people who fly a 200 kt landing.
The halfwit who spawns at a GA area or an area not meant for their aircraft so they are closer to the runway…
This has all happened on Expert Server, most when ATC was not open.
As a controller:
The moron who requests pattern work in an A388 but then just leaves to another airport after departure…
The bonehead that does not listen to the ATIS when it says ‘Rolling Departures’, and you also clear him for immediate departure for traffic on final, but he decides to take his sweet time, like your grandmother driving.
The bozo who can’t wait and enters/crosses the runway anyway.
There are a lot more, but that’s all part of the charm.