Knock-Knock (the only 3 good ones)

I love to laugh. I love a good joke. I believe there is almost no such thing as a good "knock knock" joke. I've come upon 3 that I like. To save time, I'm only going to put in the pertinent info.

1. Interupting cow
Say moo before they finish saying - "interupting cow who"

2. Nobody
Don't answer when they say - "who's there)

3. Tell them to start. Just say "knock knock" and wait.

If you actually know a great "knock knock" joke, tell it to me.