actually, i think if you took a break from the line tool, and fixed the armpit i wouldnt mind it so much :D hehe hard nipple.

Yeah... the lines are too harsh; even slim figures have curves. Major Critique ahead.
Also, his left (from our perspective) nipple seems to be sliding off his chest (Raise your shoulder like this picture; the left side of your chest will be slightly higher than the right).
And unless those things on his arms are tattoos; give them depth, cloth isn't usually implanted into the skin, make it seem as though it were wrapping around his arm.

The hand needs work also; get a friend and grab their arm like this picture; you would have to put effort into making the fingers straight like that. The quickie way to fix this problem would be to shorten the fingers until it appears that they are bending at the last knuckle, instead of the second.

Now, the shoulders again, specifically where they meet the neck; if you have a large mirror anywhere in the house (but preferably in your room) toss on a tanktop, or a tight shirt, anything that will form-fit or at least make the shoulders visible; stand with your arms are your sides in a relaxed manner, or pose like what's his name with the wandering nipple, they slope like a lumpy hanger shape (well, unless one is raised like this, but that's another story) they do not, in most cases, form an abrupt L. Inversely, the slope of his shoulder cuff (basically where the shoulder) is a little too... slopey. Unless Mr. Marik Everygayanimecat is actually some weird Cat/Alien being; his muscles (if he has any, I should hope he has some) would prevent this... instead forming a slight dip in the arm just after the inital downward slope...

This would be much easier to explain in redlining...
Simply said, the arms jsut don't have enough proper muscle accentuation; I'm not buff myself but it's obvious to tell where my muscles are in my arm.

And by the way, I don't like Yaoi, but that had nothing to do with the other problems in this picture, it's not really for you to decide who can and can't comment (you can make your own site if you want those kinds of privileges, I'm sure plenty of people would like to just say 'By the way, you can't post Yaoi pictures!' and you wouldn't think that's very fair, right?
Right.

About the anatomical problems though; they sound like a lot, but they're common mistakes.. I make'em a lot myself, but I know when they're there. Not trying to discourage you, just letting you know that... well, people aren't only negative because it's Yaoi.

Oh! Oh! I wanna point something out! Unless the ears are coming out of their foreheads (Which they shouldn't), they should be put a little bit back.