This term may also refer to a near-mythical sex act between two women. It relies on the fact that when a woman is sexually aroused, her nipples become firm and (for some women) substantially larger (men's do as well, but working from a smaller baseline).

Effectively, one woman uses her nipple -- steadied by her hands -- as an organ for penetrating the other's vagina. Obviously deep penetration is going to be impossible here, but in addition to surface stimulation, the woman doing the penetration is in an excellent position to bring her partner off with her hands. And, unlike the male tittyfuck, this stimulates the more sensitive areas of the breast, opening the possibility that both individuals will enjoy themselves.

This act is certainly performed more commonly by porn lesbians than by any real women. In pornography, any contact between an erect nipple and a vagina results in instant multiple orgasms (followed by an unstoppable urge to find a funny-looking guy and drag him in for a night of cum-drenched bisexual bliss).