I'm not a guy, but I often have a male avatar.

I would love to see items that leave the chest open, like vests and such, and weaponry that isn't several times to large for the avatar would be nice too.

Army gear would be amazing, as would general business apparel.

Ties, both tied and untied, button up shirt with an option to leave open and unbuttoned, ect.

Maybe some facial hair items, bears, mustaches, 5o'clock shadows, ect. I wouldn't wear them, but they're manly!