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Novak Djokovic at the 2011 French Open.
Since Novak Djokovic is mentioned in the headline, he has to be our No. 1 funny person in tennis.
Let's start with the obvious, his impersonations. Djokovic has become quite adept at imitating his fellow tennis players, particularly Rafael Nadal and Maria Sharapova. Not only are they funny, they're accurate.
Djokovic recently made a "Bag Check" commercial that airs on Tennis Channel. In it, he sings dramatically, in Serbian. Another popular video is of him and Andrea Petkovic, a.k.a. Petkorazzi.
Lastly, Djokovic likes to show off his humor by participating in fashion shows at the pre-tournament parties and even by performing with the Bryan Bros. Band at the 2010 Arthur Ashe Kids' Day. No matter what Djokovic is doing, you can assume it will be funny.