"The Ultimate Fighter" winner Julianna Pena says being a famous UFC fighter comes with a target -- telling TMZ Sports men have tried to pick fights with her in bars to prove their toughness.
Pena's not the first fighter to have this problem ... Cody Gibson and Michael Bisping have had similar issues -- though Bisping let the guy punch him in the stomach multiple times and made a joke out of it.
Pena, however, says guys with "beer muscles" are a real issue -- but says she's learned to deal with it.
BTW, in case you haven't seen that Bisping video, here you go ... and warning -- DON'T TRY THIS AT HOME!!!!!