Bonnar's been out of the fight game for a few years ... but The American Psycho told TMZ Sports he and Phil Baroni (another MMA great) are about to lay the smackdown in the squared circle.

"The Real Shooters (Bonnar and Baroni's tag-team) are gonna come put a hurting on you," Bonnar said. "I really enjoy inflicting pain on people."

Bonnar's first match is at a bowling alley ... but he's guaran-damn-teeing that fans will get their money's worth.

Or -- save your cash for The Legends Room ... Bonnar's futuristic, paperless strip club where you can make it rain digital dollars!