I guess this is what one would call hardcore? But I don't really see it as "hardcore yaoi," because usually manga that gets labelled like that is full of rape and other unpleasant stuff. Which leaves me in a pinch, since I enjoy, shall we call it, explicit(?) yaoi, but I hate those rape tropes. Ikenai Otoko is certainly explicit (actually, explicit might be an understatement). Well, it is about a guy named Ryuo who is told by his boyfriend that he is lousy in bed, so he decides to become a porn star to learn; I guess he means learning new techniques :D (yes, becausethat would be the solution any person would come up with in this situation :P). Thus, if it wasn't explicit it wouldn't really fit it's subject matter. But though the premise sounds a little silly, Takao sensei actually pulls it off really well.
Don't be fooled, there's no character development and the such to be found here. But that's not what Ikenai Otoko is about. This manga is more about how we perceive sex. Are porn stars immoral because they normalize sex? Why should sex not be normal? What's the difference between sleeping with a friend and sleeping with someone you love?
These might not be the usual questions we see in a manga, but just because they are unconventional doesn't mean they are of less worth. Speaking of unconventional, who doesn't love a short seme? Or a tough guy who'd "never bottom," but then gets swept away by his carnal pleasures? :D

However, I think it's only a fair warning that this manga can be seen as provocative if you're used to the "Only You, I Am Completely Obsessed" yaoi or "If It's You, It's Okay" trope. In this manga, sex is casual, like playing tennis ;). So there are threesomes.