I love the question "Do we have any evidence that this is traditional." This thread alone is all the evidence that I, for one, require. Besides, I have made a personal hobby of collecting this song from kids since I was a kid myself. In 1972, I heard a great version from an elderly Native American in a nursing home.

Great big gobs of greasy, grimy gopher guts,
Mutilated monkey meat,
Little birdies' turdy feet.
French fried eyeballs floating in a pool of pus.
...And I forgot my spoon.
...But I have my straw.

The singer made little hand gestures demonstrating the pulling of the guts, the mutilating of the monkey meat, etc. The performance was a classic and enthusiastically applauded by other residents and the nursing staff.

I believe the respondent who reported learning "Gopher guts" in Karachi was correct in linking this song with "Don't ever laugh when a hearse goes by" since it is rare to collect the one without the other. I believe that "Nobody loves me, everybody hates me, I'm going out and eat worms" is also linked. I'm sure this material has been well published, however. Has anyone done a literature search?