
..."Don't KNOCK on my door before 11:00
or I punch you in the throat" rule.
The Big Bang Theory Season 2, Episode 18

This is the secret KNOCK:
The Big Bang Theory Season 1, Episode 16

Knock or ring?
Unh!
Breaking Bad Season 4, Episode 4

-(KNOCK ON DOOR)
- BERT: Hello? Anybody home?
The Big Bang Theory Season 10, Episode 21

(KNOCK ON DOOR)
The Big Bang Theory Season 1, Episode 4