You know your...

You use 'you know your...' to let your speaker know you're about to say something funny. By using 'you know,' you are also trying to get the speaker into your corner, so they will relate to you.

Example:
-You know your cell reception is bad when you get a text message 5 hours later!
-Yeah, that's pretty bad!

Yo!

"Yo!" is a very informal, familiar greeting, kind of like "Hey!" It can be used when you don't know or can't remember someone's name and want to get their attention. Another possible use is as a shortened form of "your." It originated in African American Vernacular English (AAVE), but has now been adopted by speakers of all ethnicities. It is interesting to note that "yo" also means "I" in Spanish, a language widely spoken in the U.S., but in American English it doesn't mean that, nor is it related.

Examples:
-Yo, come back here!

-Get to work, yo!

-Yo mamma!


True story:
I'm white. Sometimes when I call my dad on the phone and he sees it's me on the caller ID, he answers, "Yo!"