Farrah Abraham -- My Sex Tape Co-Star Has a Small ...

Farrah Abraham is so pissed that James Deen blew the lid off her sex tape scheme, she went straight for the jugular when expressing her feelings about him -- and by jugular, we mean his manhood (and by manhood, we mean penis).

The "Teen Mom" star has been in a war of words with Deen ever since he told us that Farrah's "sex tape" was really just a porn shot at her request.

Farrah took a below-the-belt shot at Deen while talking to our photog yesterday ... which is ridiculous and gross -- ridiculous because he's a male porn star (um, hello!?!?!?) and gross because her mom was standing there the whole time.