"I have lost my underwear" was a song made up by David Graham of Christchurch New Zealand in the 1970s, to the tune of "Bye bye blackbird". The version given here is probably distantly derived from it, as there are lines that don't make sense here, but did make sense originally. It went -

I have lost my underwear, I don't care, I'll go bare.
Bye bye, long johns.
[You were always close to me], tickled me, tee hee hee!
Bye bye, long johns.
How I loved that little trapdoor behind me,
You all knew exactly where to find me.
I have lost my underwear, I don't care, I'll go bare.
Long johns, bye bye.

Not a hundred percent sure of the bit in square brackets, but think it's right.

pelliondance