Alex Pettyfer pissed off a group of jacked up dudes working out at Muscle Beach in Venice ... and we got video of their heated exchange.
Pettyfer was passing the famous weight lifting hangout when he asked the guys working out how much they lift. For some reason, a few of the lifters took offense ... and both sides started arguing.
In the video, one of the lifter accuses Alex of talking "s**t" ... which the "Magic Mike" star adamantly denies.
Oh, and that's not really a fight, it's an argument.
