He's inseparable from his pet poodle Pierre. When Pierre wasn't allowed in Wimbledon in 2011, a source told the Telegraph, "Whenever he can he takes the dog with him, he is genuinely upset. For him this is a very serious issue."
He talks to himself while he plays, and once yelled out loud in Serbian, "Now you all will s**k my d***." Recently, he yelled at a ball boy who startled him during the Miami Open. He later apologized for the incident.
He tends to feign injury if he gets down in big matches, and has been accused of pretending to be hurt by multiple opponents. Recently, his antics at the 2015 Australian Open landed him under speculation of faking an injury during his match against Andy Murray.
He used to impersonate fellow players, including Rafael Nadal, Serena Williams, and Maria Sharapova. He even did one of his coach, Boris Becker.
Here's his best Sharapova impersonation:
He furtively eats bananas during changeovers.
He's obsessed with dancing, in all forms. He even attributed his dance moves to helping him defeat Andrey Golubev at the Dubai Duty Free Tennis Championships earlier this year.