We had a discussion at lunch today that any joke you have to explain is one that has failed.
Now, moments ago, in the hallway:
Established Astronomer 1: "It's like 'Groundhog Day'."
Other Astronomer: silence
EA1: "You know, because I saw you in the hall before and now I saw you again."
OA: silence, walks away
EA1: "The movie with Bill Murray."
OA: nervous laugh, quietly and semi-sarcastically "yeah, that was a good movie"
OA: practically runs the rest of the way down the hall.
Gotta love working with such great folks.