F.A.R.T. the Movie
From the F.A.R.T. the Movie wiki page:
F.A.R.T. the Movie, released in 1991, is about a man named Russell who is obsessed with farting. His girlfriend Heather despises farts and becomes angry with Russell because all he does is watch television and fart. She tells him that if the television turns into fart jokes, then Russell won’t even leave the house. Then one night, the television does become all about farts.
The movie stars Joel Weiss as Russell, and Shannandoah Sorin as Heather, and was written and directed by Ray Etheridge.