"YouTube news" is another way of saying "old news" or "I already heard about it". If someone tells you something that you have already heard about, you can respond by saying "YouTube news".
This phrase communicates that, like news that spreads throughout the universe very quickly via YouTube, you have already heard about it. It takes 5 minutes for new news to mature into YouTube news (aka old news).
Thanks to YouTube (and texting), news gets old really fast. YouTube news is new news that is already old. However, YouTube news does not have to refer to things that are ACTUALLY on YouTube. "You Tube news" usually refers to things that only matter to you, your personal friends, and the fake friends you have on facebook.
HOW TO USE THE PHRASE:
You usually just say, "YouTube news" without any other words accompanying the phrase. The words "YouTube news" explain exactly what you mean all by themselves.
If it has been 5 minutes since an event, there is a 99.9% chance that EVERYONE who could possibly give a shit about it already knows every damn detail (thanks to texting). Consequentially, the phrase "It's been 5 minutes" can be used in conjunction with the phrase "YouTube news".
MARY: Guess what! Johnny and I got engaged!
BILLY: YouTube news.
MARY: But he only proposed 5 minutes ago.
BILLY: Yeah, I know.
JILL: You're never going to believe this: Heather's car broke down in the middle of the Siberian tundra and she almost froze to death.
BOBBY: YouTube news. It's been 5 minutes.
MARK: Dude, I spilled my coffee on an old lady and she burned to death.
JOHN: It's been 5 minutes. Already heard about it.
MARK: Damn YouTube news.
OSCAR: Hey man, you're never going to believe this! I got a call from... oh yeah, it's been 5 minutes. You already know about it.
JACK: Yeah, YouTube news.