So, what are your theories on the background in Salad Fingers?
Salad Fingers himself often refers to "The Great War", and this might mean that his world was destroyed during a huge war long ago.
Who knows, maybe Salad Fingers once was a perfectly normal guy, but he suffered some extremely traumatic accidents.
He probably lost his family and felt lonely and desperate in the desolated world, until he became completely twisted.
As a matter of fact, in the newest episode he breaks apart several times, and he obviously greatly misses something.