You wouldn't know a good time if it bit you.
4 seconds sound clip from the Vacation (1983) movie soundboard.
You can hear this line at 01:09:38 in the DVD version of the movie.
Quote context
[...]
- All I know is I'm trying to treat my family to a little fun.
- Oh, spare me. I know your brand of family fun.
- You wouldn't know a good time if it bit you.
- No. Ahem. Do you mind if I sit down?
[...]