John McEnroe - You cannot be serious!

John Patrick McEnroe Jr. is a former World No. 1 professional tennis player from the United States. Besides his great shotmaking artistry, he is remembered for his confrontational on-court behavior, which frequently landed him in trouble with umpires and tennis authorities; and for the catchphrase "You cannot be serious!" directed toward an umpire during a match at Wimbledon in 1981.

A serve-and-volleyer, his super talent enabled him to dominate tennis from 1981-84. He dethroned Bjorn Borg at Wimbledon, winning three championships on the prestigious grass courts. McEnroe won seven Grand Slam singles titles.