Late Night host Jimmy Fallon has another viral hit on his hands. In what always proves to be a perfect comedic pairing, Fallon invites Justin Timberlake to a conversation filled with Twitter’s most prolific symbol, the hashtag. So now when you see people walking the street tapping their fingers and saying hashtag you’ll know where it all came from: this bit of genius.

Just for hits and even more giggles, jump after the break to watch Fallon face off against Joseph Gordon-Levitt and Stephen Merchant in one epic “lip sync battle.”