All the clocks in the pawn shop in the movie Pulp Fiction are set to "4:20".
Not all the clocks in the movie are set to 4:20. For instance the watch that Christopher Walken gives to the little kid is not set to 4:20. Most people watching the movie don't notice this, since they're too busy wondering "how did Christopher Walken fit a watch up there?"
If you didn't already know, 4:20 is a popular term used in the marijuana culture, usually referring to a time to smoke marijuana. The origins of "420" are disputed, but it first started becoming popular in the 1970s.
Other weird 420 facts? Albert Hoffman took the first intentional LSD trip at 4:20 on April 19, 1943. The score of the football game in Fast Times at Ridgemont High was 42-0. Hitler was born on April 20, 1889. And the Columbine massacre was on April 20, 1999.