Game rule one: All couples must be boy girl.
6 seconds sound clip from the Grease (1978) movie soundboard.
You can hear this line at 01:09:49 in the Blu-ray version of the movie.
Quote context
[...]
- Mr. Vince Fontaine. Mr. Vince Fontaine!
- Hiya, kids. Hey, it's great being here at Rydell High.
- What's your name, sweetheart?
- Game rule one: All couples must be boy girl.
- All right, all right, come on.
- And rule three: Anyone doing tasteless or vulgar movements will be disqualified.
[...]