American Football, just for the simple fact that for one hour of game play, there's three hours of nothing but guys standing around scratching their asses, and what with all the padding and helmets, there's not even any eye candy to keep you interested...
Golf, is there anything more boring to watch?
Tennis, again BORING!
NASCAR/Indy racing, just driving around in circles in machines the barely even resemble cars. You pry for an accident just so there's something interesting to watch. It was so much better in the old days when drivers raced real cars, they didn't bring them in on trailers they drove them to the track and then drove them home after the race...
I love to watch...
Gymnastics (male), being a former gymnast myself, I understand it well, gymnast have the best bodies, and it's great when you can see all the muscles at work...
Wrestling (college) the most basic of athletic competition and plenty of eye candy, especially on the sidelines after the match is over when they strip to the waist...
Swimming/diving, speedos, eye candy galore, never gets boring...
Rugby and Ice Hockey, just for the sheer physicality of the games...