Fairly common in overweight males. As the guy gains more and more weight, he appears to develop cone-like bitch tits. Usually accompanied by wordmotherly nipples/word.
A common occurance in drunken sexual encounters, the smearing of fecal matter on a womans bust, usually inadvertant, while attempting to dunk your nuts in her mouth. Usually associated with poor balance and easily avoided with a tactful dunking stance.
Ben- dude i really pooped shit up last night Jack- what crappened?
Ben- I was trying to squat my nuts in my girl's sack hole, right? i fuckin lost my balance, fell back and gave her the ol' poop tit
Jack- aww dude
Rock tit is what happens to your nipples when they get cold, or in some cases, when one gets horny. Rock tit is characterized by a sudden hardening of the nipples, hence the name.
More "severe" cases of rock tit, where ones nipples are so hard they could shatter bones, is named "Diamond tit".
Joe: Dude, you should have put on a better shirt for today.
Hal: Why's that?
Joe: It's cold out and I can see your rock tit.
Hal: Aww shit!
Joe: Attractive.