What’s up with Joaquin?

River’s little brother has been behaving oddly recently. Check out his appearance last week on Letterman:

 

Rumour has it that it’s all part of a Spinal Tap-style mockumentary about Joaquin’s burgeoning hip-hop career.

It could well be. Casey Affleck has been following him around with a camera and if you check Dave’s Unabomber gag at the 3-minute mark, it definitely looks like Joaquin’s holding back a laugh.

If it is a joke, it’s damn funny.

If it’s not, then . . . well.