Were the breasts doing anything sexual? Was there a cucumber or obvious penis (or lesbian equivalent) attached in an erotic position?
If not, then screw youtube and screw the morality that says that the female body is an inhherently adult-only product. You never see photos of topless guys flagged as NSFW do you? So why women?
I konw it sounds like I'm making a mountain out of a molehill but it all adds up. Slowly but surely, masculinity becomes 'the standard' and femininity becomes 'the other' - the stuff that is NSFW and should be shuttered away in the corner. One more brick in the wall that says 'men are normal, women are sex objects.' That offends me far more than any glimpse of the female body ever could. I wonder if I could get the relevant 'NSFW' warning tagged 'NSFW - contains sexism and double standards'.