All of Harvey Pekar's appearances on Letterman
They must have had a sort of permanent parting of the ways, because he stopped appearing in the mid-90s - they were an interesting pair to see interacting. Letterman sort of does backflips, as he does these days, apologizing for his handling of a guy who was rather cantankerous by any measure. I think Dave is kind of a guilt-freak.
https://www.youtube.com/watch?v=biOodnioY8c
more background :
https://www.phactual.com/the-story-behind-harvey-pekars-infamous-last-letterman-interview/