dvdclon
Second Unit
Actors portraying rockstars/popstars playing a guitar (or piano), where it is obvious they're not playing the correct notes + chords on the guitar (or piano) corresponding in the accompanying music in a scene.
This is especially noticible if you know what the note/chord patterns are suppose to look like on the guitar neck or piano keyboard corresponding to particular note/chord sounds in a piece of music.
To my eyes as a former musician, it is very aggravating to watch and notice such deviations.
Related to this is when people go to see a singer performing, the singer just finishes a song, hands off their instrument (if any) to a nameless bandmate and then sits down to talk with the visitors, leaving the poor band to fend for themselves.
Having been in "poor bands," this offends me mightily!