Ben Stiller Surprises Audience as Derek Zoolander at Film Screening

Ben Stiller is bringing "Blue Steel" back ... surprising a packed crowd of "Zoolander" fans as his infamous character.

It all went down Saturday night in Los Angeles, during a special screening of the 2001 cult classic at the Hollywood Forever Cemetery.

Ben -- or should we say Derek -- turned heads by greeting the audience before the movie started ... delivering a hilarious bit as he thanked the crowd and mispronounced the show's organizer, Cinespia.

He joked they had the "courage" to have the first-ever 9-year anniversary screening of "Zoolander 2" ... which, as you'll recall, was a box office flop.

Stiller then told the audience, "Don't get freaked out by all those creepy gross dead people underneath you" ... of course, referencing the thousands of people buried at the historic cemetery.

The surprises didn't end there ... Stiller was interrupted by "Severance" star Tramell Tillman, along with the USC marching band ... and the crowd ate it up. You'll recall, Stiller is also the director and EP of the hit Apple TV series.