It's a routine between Abbott and Costello. When you do it, you're not funny. You're the comedy team of Abbott and Abbott.
7 seconds sound clip from the Rain Man (1988) movie soundboard.
You can hear this line at 01:10:49 in the Blu-ray version of the movie.
Quote context
[...]
- You're never gonna figure out who's on first base, because Who is on first base.
- That's a joke, Ray. It's comedy.
- Sometimes his wife comes down and collects it. Whose wife?
- You got a first baseman on first? Yeah.
- You understand what I'm saying?
- Sometimes his wife comes down and collects it. Whose wife? Yeah.
- If you understood that, if you understood that it's funny, you might get better.
- All I'm trying to find out is, what's the guy's name on first base?
[...]