To me, the favicon merely looks like a sumo wrestler’s head with a short ponytail and scowling/serious eyebrows. I can’t tell what NSFW thing you see it as.

Spitballing here, but it could be a POV dick's eye view. I am really reaching however.

edit: Interesting downvotes, I dont mean to be rude, I am just trying to see what someone could find offensive. (I dont see the problem with the favicon)

Until I read this thread I also saw a sumo or an angry onion, but I believe the picture is actually a person facing away from us undoing their kimono.

You see all that in a 32x32 pixel image?

It's much larger than that http://kimonify.kimonolabs.com/favicon.ico