The breasts of a nun or other female member of the clergy. This expression is most commonly used when your buddy decides to drive like he is Dale Earnhardt himself.
Josh, "Hey, We should go left!"
-tires squeal as Josh yanks the car into a power slide-
Sarah, "Holytits!"
My bro came up with this, basically when something is so appalling or astonishing that "Holy shit!" or "Holy fucking shit!" wont cover it
Heres an example of "Holy Tits!" in a conversation
Jimmy: "Bro, look at him! he's lighting firecrackers in front of that guys house!"
Tom: "Wait, isn't that principal Skinners house?"
Jimmy: "Holy Tits!!!"