I was not amused, and instead of explaining myself, I'm going to quote a reader from a different forum, who said it more eloquently than I ever could
"If you find it hilarious, great. I’m not trying to change your mind. I posted that I thought it was sexist because sometimes it’s nice to tell other lonely dissenters that they’re not crazy.

And I’m still not trying to change anyone’s mind, but I’ll try to clarify where I’m coming from. To me, the basic joke of that video is having a guy act out all the ‘annoying things girlfriends do on mountain bike rides with their boyfriends.’ I don’t see it portraying annoying rider behavior, I see it portraying annoying female rider behavior. It’s supposed to be funny because it’s a guy doing it.

To me, this video ridicules women. I’m put off by it the same general way I would be by a video of a black man and a white man where the white guy is eating fried chicken and watermelon and leering at the black women. Or a Jew and a WASP and the WASP is trying to squeeze every last dime out of the Jew. Or a gay man and straight man and the straight man is lisping and fondling 5 year-olds.

Now, those examples are all a lot more offensive to me than a whiny hormonal boyfriend on a bike, but the basic premise of the humor--“isn’t it a riot when a #1 does all the bad things #2s always do”--seems the same. I’m sure some people would think all those videos are hilarious and clever and demand that anyone not laughing lighten up. Just not how I see it. "