We’ve been laughing at these all week. Two Late Night vids have snagged millions of YouTube hits. The first pits Jimmy Fallon against his old ”pal” Justin Timberlake in a #hilarious hashtag-off. The worth-it moment: when Questlove makes his #bigentrance. The other vid, dubbed a ”Lip Sync Battle for the Ages,” sees returning champ Stephen Merchant take on newcomers Fallon and Joseph Gordon-Levitt in a faux singing contest that turns into a wild-eyed, gyrating, microphone-stand-twirling spectacle. Highlights: Merchant’s “Boom! Shake the Room” and Levitt’s “Superbase.” But don’t let us spoil the show.