"Coward!"
That's Julianna Pena's reaction to Amanda Nunes' retiring inside the Octagon after UFC 289 ... walking away from the sport before the two UFC stars got a chance to fight for a third and deciding time.
The former bantamweight champ joined Babcock on the "TMZ Sports" TV show (airs weeknights on FS1) ... where she viscerally reacted to Nunes' retirement.
"There's unfinished business and listen, the reality is that Amanda retired. She had a great career, but let's call a spade a spade. She's a coward.