knock, knock

who's there?

...boo. boo, who? ah, don't cry.

...tank. tank, who? you're welcome.

...who. who, who? hello, mr. owl.

...ivan. ivan, who? ivan workin' on the railroad.

[and let's not forget the classic]

...banana. banana, who? [repeat at least ten more times, preferrably until your sister/brother is driven to tears, violence, or both] knock, knock. who's there? orange. orange, who? orange you glad i didn't say banana?