Reading some of these makes me realize even more how lucky I am. My singer/songwriter/r. guitarist would never tell me how to play my bass. In fact, when I first auditioned for the band, they had given me a few recordings to learn. There was one were I completely changed the bassline, and the response was "Wow, that actually sounds like something a bassist would play!"
Anyway, things that irk me:
-Guitarists not knowing the notes on the fretboard, instead referring to them by fret and string. Particularly annoying when they're in an alternate tuning.
-"Well, bass is easier than guitar because you only play one string at a time, right?"
-Drummers randomly going into a flashy, grooveless fill when you've spent half the song locked together. Throws me off my game like nothing else.