Michael Sam Arm Wrestles Fashion Designer, 'This Guy's a P***y!'

Michael Sam went straight "Over the Top" in a Dallas bar -- arm wrestling a dude who called him a "p*ssy" ... and TMZ Sports has the video.

Here's the deal ... Sam (the 1st openly gay player to be drafted by an NFL team) was hanging out at Bottled Blonde when he started chatting it up with Miami designer Jared Lang.

Lang playfully challenged Sam to a test of arm strength -- and Sam obliged. They clasped hands, Lang teased Sam by jokingly calling him a "p*ssy" ... and then it was on!

Sam was clearly in control the entire time -- and casually provided resistance while Lang used his body weight to slam Michael's hand down.

At one point, Sam was watching TV while Lang struggled to get the upper hand.

Sam eventually loses (seems like he let the guy win) ... but the 2 were cool and dapped it up afterward.

But here's a warning -- CAREFUL WHEN ARM WRESTLING ... remember what happened when Larry the Cable Guy did it ...