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.
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This is the theatrical trailer without watermarks.
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This movie actually didn't come out until 2000, but here's the trailer anyway, originally posted to YouTube by TLAVIDEO.