Speaking of pet peeves...
in doubles, when you hit a solid volley and/or multiple volleys and your partner is immobilized at the baseline watching the ball go back and forth. In theory, your partner should be using every free second to reposition.
Imagine sticking an aggressive volley and having your opponent on their heels, but allowing them to loft an easy defensive shot to your unassuming doubles partner waiting to hit a groundstroke at the baseline. Gross.