I sing this song occasionally, usually when children are around: the mentions of a*rseholes by an adult always raises a giggle or two.

Most of the versions above correspond roughly to the one I know, except for the last verse, which I learned as follows:

...and that's the reason why, sir
when walking down the street
and that's the reason why, sir
when doggies chance to meet
and that's the reason why, sir,
on land or sea or foam.... (spin out this note as long as you can!)
They'll sniff each other's a*seholes
TO SEE IF IT'S THEIR OWN!

Ah, happy memories...