Djokovic is well known for his impressions as he became quite popular many years ago for doing them. He was doing player impressions for a while after his matches but eventually stopped out of respect for his colleagues. He still got it as he demonstrated recently by impersonating Snoop Dogg in Monte-Carlo during the player's party and now he imitated his coach Ivanisevic.
It was a practice session at Roland Garros with Djokovic imitated the famous Ivanisevic serving motion. Check out how it looks like below.