Dude, Where’s My Car?(2000)
Jesse and Chester, two bumbling stoners, wake up one morning from a night of partying and cannot remember where they parked their car. They encounter a variety of people while looking for it, including their angry girlfriends, an angry street gang, a transexual stripper, a cult of alien seeking fanatics, and aliens in human form looking for a mystical device that could save or destroy the world.
This is the theatrical trailer without watermarks.
This movie actually didn't come out until 2000, but here's the trailer anyway, originally posted to YouTube by TLAVIDEO.