She's already nailed the cheesy dialogue -- and now former soap opera villain Kelli McCarty has decided ... she just wants to be nailed.

The former Miss USA 1991 -- yeah, she was a frickin' beauty queen -- has quit the mainstream acting biz for a shot at a career in "adult entertainment."

McCarty, who played maniacal Beth Wallace on "Passions" for seven years, is now a "Vivid Entertainment" girl -- and has just wrapped on her first XXX feature, "Faithless," in which she plays the lead character to a very very supporting cast.