When I first read this comment, the language seemed confrontational and harsh to me (especially since the user's so friendly in his comments), but then I realized you're right.
Posting sexual selfies on a meme site where there are young teenagers present is just wrong. On top of that, to post flirty comments on other users' memes to encourage them to come back to look at your photos is even worse (especially when those users' ages are not known), which is something I've also seen.
I would also say I don't think it's just a man vs. woman issue (though it's true our society does have different standards for how men and women's bodies are displayed). The reason I'm saying this is because I think if there were a woman engaged in similar behavior (posting photos of herself in skimpy outfits on a site with young users, and putting seductive comments on other users' memes to draw them to look at her memes), she would be wrong to do it, and there would be pushback. So I don't see why we should give this user a free pass (either because he's male, or because he's friendly in his comments, or because we're used to it, or whatever other reasons we might think of to overlook such behavior).
And yes, it's true that a lot of users (including myself) make dirty jokes, or posts that have sexual themes, but when it comes to putting up real photos of oneself, it's a different topic entirely.
I have no personal animosity towards this user (at least not that I'm aware). He has never behaved in an unfriendly manner towards me. What people do in the privacy of their own homes is up to them. People also have the right to wear whatever brand/style of underwear they want. But when a person is submitting content to a community, it's important that they make the attempt to respect the basic mores of that community.
The expectation that parents have that their children can go onto a meme site without seeing photos of a grown-up posing in his underwear, or without receiving comments on their memes that come across as an older person trying to engage them in sexual conversation, are some of those basic mores.
A person can be proud of who he or she is, without posting semi-naked photos on a site for children to see. I hope this user understands it's important to respect the standards of a community (whether he personally agrees with those standards or not), and I hope he tones down his act significantly out of respect for other users on the site (especially the younger ones).