You don't need to be attacked directly to feel bad about something, and "just don't be sad/upset" is really shitty advice for dealing with a society-wide issue.

Re: penis size, when it's a popular joke in movies and TV shows, and people gossip about how small and disappointing someone was behind their back to each other, it doesn't matter if no one says anything directly to the person like "haha your dick is small"; they can see the big picture around them and feel bad about themselves. Like, this is literally the issue with stuff like "unrealistic portrayals of women in media" where everyone is skinny and gorgeous and photoshopped. You can see social values around you without having anyone directly tell you that you don't match up to them.

"It's hard to change other people, so don't bother trying" isn't a sufficient answer. "The world sucks just suck it up" means nothing gets better.