Corn's A Poppin'
This is a movie that's going to be hard to sum up because it's so... perfect for riffing.
It's a semi-musical film (about an hour long) about a popcorn magnate who needs to boost sales of his product, so he produces a TV musical variety show to promote it. What kind of music? Country music, of course! However, the PR guy is secretly working for a rival popcorn company, so it's up to the TV show's host and his whiny little sister to save the day. All this...and much more...written by Robert Altman.
I have a few links to help prove my case that this is prime riffing material. First, this recent review of the film by Huffington Post: http://m.huffpost.com/us/entry/5536972
Someone in Detroit taped this movie off TV back in the day and it's on YouTube now. It has to be seen to be believed - SERIOUSLY, though the age shows: https://youtu.be/QzejNljcss0
You'll be happy to know that the movie has been recently restored, and here's a link about that -
You KNOW you can't resist something this corny from the 50's!