It's not always possible for an audience member to catch every single detail in a movie or understand every reference in a comedian's monologue. Some jokes or clues or other obscure details might only begin to make sense on the way home from the theater or after a second viewing. This kind of epiphany after the fact is often called a way homer, since that is the precise moment many audience members have it, on the way home.
A way homer can be a background detail or a cryptic bit of dialogue which doesn't appear to make sense during the first viewing. A movie about a raging alcoholic, for example, might include a scene where the main character watches a classic film on television. The scene may not make much sense at the time, but on the way home the viewer might realize the clip was from a classic alcohol-themed movie such as The Days of Wine and Roses. The reference would be considered a way homer.
A comedian may also deliver a more sophisticated or cerebral joke during his stand-up routine that may appear to bomb with the audience at the time. In actuality, the comedian would most like call the joke a "way homer" because he knows some audience members will get the real gist of the joke on their way home from the show. While it might not be a good idea for a comedian to fill his or her act with cerebral or obscure jokes, the occasional "way homer" can be very effective. Comedians such as Sara Silverman and the late Mitch Hedberg are well-known for their use of obscure references or intellectual humor.
Some movie makers such as the Coen and Zucker brothers are famous for including a number of way homer moments in their films. It may take several viewings in order to notice all of the in-jokes, movie spoofs and pop culture references in movies such as Fargo and Airplane. In the Alan Parker film The Commitments, all of the posters displayed in the video store promote actual Alan Parker films, a detail many viewers may miss the first time. Almost every episode of the sitcom Seinfeld contains at least one reference to Superman, which would be another way homer detail for those who view syndicated reruns of the show.
A way homer moment can often be a satisfying intellectual or pop cultural "snack" after enjoying the broad strokes of a well-crafted movie for the first time.