Farrah Abraham -- I Didn't Get an STD from James Deen

Farrah Abraham clearly has STDs on the brain ... 'cause that's all she wanted to talk about last night.

The "Teen Mom" star was outside Katsuya in Hollywood ... when we asked about her new 6-figure endorsement deal for a weight loss product.

The fun part -- we asked if she was present for lab testing (on the product) ... but Farrah thought we were talkin' about her vagina. She was very forthcoming, as usual.