The cunt punt is firmly rooted in pop culture:
etc...
It's always considered a low blow just like a kick in the nuts, where a "fair fight" means you don't go below the belt. When people are portrayed doing this, especially men, they are shown to be cowards or ruthless bastards.
Not sure on "tit hits", but I suppose it's as taboo as crotch shots. I know if some random woman came up swinging on me for no reason, I wouldn't be going for a cunt punt or a tit hit. Doing that is...well it's just wrong.