Because humor is a natural part of any sort of conversation that goes around here, Lion.
I don't know about your household growing up -- maybe everyone goes around the dinner table saying, "School was fine, but here's a picture of mom's naked ass!" However, I bet you'll find yourself in the minority around here.
Not to mention that we have underage kids on the forums, and that people often post while they're at work... and many of those photos are NSFW.
Sorry, but equating a funny picture with some woman's spread ass ain't in the same f*in' ballpark, it ain't the same league, it ain't even the same f*in' sport.