If you think I'm trying hard to find borderline examples, you're mistaken. They're everywhere. They fall off the tree as soon as you start thinking about them.
See: This famous painting of the Sistine Chapel by Michelangelo that depicts a completely naked male. Despite the exposed male genitalia, this art fully complies with Imgflip TOS.
You might say this image would also be okay under your anti-erotic bill because the primary purpose of this art is religious. I don't know.
I might say the primary purpose of the two images of the girl and dude in their swimwear I posted above is simply to sell a swimsuit. And as a matter of fact I'd be right - these images are both simply taken from swimsuit ads.
Erotic? Really?
I might also say that the primary purpose of the OP meme we're commenting on of the woman holding an American flag while also wearing an American flag in swimsuit form is patriotic, and the text I added is inherently concerned with roleplay of this stream.
And you might agree with everything I said, or you might disagree with everything I said, or you might agree with some of what I said and disagree with other aspects.
Isn't all that an indication this subject isn't quite as cut-and-dry as it might seem?