The way I heard the song goes like this:

And then there's Grandma,
Swingin on the outhouse door:
She's in her nightie!
Swingin on the outhouse door:
She'll get a splinter!
Swingin on the outhouse door:
And then there's Grandpa,
Sayin more more more!

It might just be the version my generation has come up with but I find it rather amusing =)