As the cofounder of a startup, I agree that a no-bullshit attitude is important. However, respect for one's coworkers is definitely not bullshit. Startups are hard and they're a team sport. If you aren't continuously looking out for your colleagues, they company's probably fucked.
The point isn't "nobody can object". It's that nobody gets hurt. We laugh a lot at work, but it shouldn't ever be at the expense of somebody's feelings. Sexism is a real, actual problem. Reinforcing it, even accidentally, can be hurtful.
As for examples of better sorts of humor, consider Bill Bryson. Most of his funniest material is about himself. Or consider the show Archer. They work with a lot of edgy material, including some obviously sexist and racist bits. But they use that to call out and deflate the sexism and racism. Or watch Louis CK's bit on being white:
And I challenge to provide a joke nobody can object to.