It's on like Donkey Kong!!!
Here's the story:
This one time, Jonah Hill was at a party and he saw Chace Crawford and Matthew Morrison talking across the room. Being a creeper - and a huge Gossip Girl fan - Jonah decided to eavesdrop on the fella's conversation. What he heard was his named used as the bunch line of a joke and that, in word, displeased him. He took his beef to Jimmy Fallon and challenged Matt to "bring his shi*t" the next time their paths cross.
Then, things got REAL!
Check out the video (above) to see Matt's response to Jonah. All we'll say is that JH better take some tap lessons or something, because Matt may have the high-kick leg up on him, if you know what we mean!