You know damn well who it is!
3 seconds sound clip from the Animal House (1978) movie soundboard.
You can hear this line at 01:42:11 in the Blu-ray version of the movie.
Quote context
[...]
- Daddy! Mom, Dad, this is the boy who molested me last month. We have to get married.
- We should discuss this some other time, sir. I know that you're very busy...
- Come out of there! Come out of there, you bastards!
- You know damn well who it is!
- I'm sorry, you'll have to come back later, I'm doing the dishes.
- Excuse me! Pardon me! Pardon me!
[...]