Matt Dillon -- Code Name Joe

Maybe Matt Dillon should have been considered for the "Mission Impossible" spy role instead of Tom Cruise -- because he's gone undercover!

The normally serious and always depressed-looking actor was spotted at a Coffee Bean by a TMZ staffer over the weekend, and instead of giving the barista his real name, the super slick Dillon told them his name was Joe.

Yes, he's that lame.