The other day I watched Windy City Heat (2003).
I was recently reminded of this movie by a podcast, although I don't recall which. This is a movie about a prank on an actor where everyone involved got him to believe he was the star of a movie that seemed to be written specifically for him. The jokes and the scope of the prank are pretty funny, although I'm not sure I buy that it's a genuine prank. I was trying to find some follow up on the people in the movie on youtube and found a clip from before the movie where the main character is seen on screen with Cousin Sal from Jimmy Kimmel/ Bill Simmons entertainment. In the movie, Cousin Sal plays a lawyer who negotiated the main character's contract and that character references him again later. It's pretty clear that he knew him before he played that character, but overall, it's an interesting take of making a movie out of a grand prank.