If you've ever wondered how shojo manga, which is aimed at young women, is different from tough guy manga, which is aimed at young dudes, then these comparisons should make it totally clear.
You probably know what shojo manga is. Classic examples include Sailor Moon and Boys Over Flowers.
In Japanese, "tough manga" is "kouha manga" (硬派漫画), with "kouha" referring to "tough," "strong," or even "rowdy." A classic example would be Fist of the North Star.
To be honest, I haven't really heard the term "kouha manga" used widely as a genre per se (I mean, it's easily understood), but recently Japanese television show School Revolution! compared scenes in shojo manga and kouha manga.
Via Twitter user IcePink375, here is a kiss scene. (The shojo manga is on your left, and kouha manga is on your right.)
Bathing scenes in each.
Comparing how a slap to the face is depicted.
So basically any manga in which people's heads get sucked off or explode are tough. Noted!