Just looking at the other answers and I realise that I'd forgotten basketball. I've tried, I've been to a few NBA games, and I admire the athleticism, but I simply can't bring myself to care about a sport that has so many points in it. The beauty of football is that most goals are important...
Rugby. Never watched an entire game, never intend to. Most motor sports.
I'll watch tennis if I'm paid to.
Sailing might be a laugh to take part in, but watching it is dull.