Visible crew/equipment: As the camera shot moves up Ironman, you can see the reflection of the camera crew in the chest area.
Visible crew/equipment: During the musical when Will is singing about "Hop Sing", and the Asian guy with glasses appears next to him, you can see the reflector screen reflected in his glasses. (00:17:15)
Visible crew/equipment: When Jonah tells McLover they have to steal the booze, and McLover says "I am McLover", you can see the reflector screen reflected in McLover's glasses several times. (00:11:10)
Answer: It's a spoof of the Sarah Silverman song called "I'm F**king Matt Damon", plenty of versions to view on YouTube.
GalahadFairlight