John Leguizamo isn't pulling a Dean Cain and volunteering with U.S. Immigration and Customs Enforcement ... he says that's for losers.

The actor hopped on social media Friday and blasted the 'Lois & Clark' star for supporting ICE, volunteering to become an officer and helping boost their recruiting numbers.

John says Dean is a loser and a moron for volunteering to help deport illegal immigrants ... and then he hits Dean with the big blow ... telling him his pronouns are "has been."

Ouch. Play video content

As you know ... Dean took to social media earlier this week, urging his followers to sign up as the agency worked to recruit loads of new officers.

Dean then joined us on "TMZ Live" and doubled down ... saying he's joining to back law enforcement officers who, in his

See Full Page