This one I got from my grandfather:

Singin' in the bathtub Singin' for joy Singin' the song of Lifebouy Can't help singin' 'cause I know Lifebouy really stops ... B.O.

This one's from my own memory:

Bum, bum, bumble bee, bumble bee tuna I love bumble bee, bumble bee tuna ... (and so on)

Weirdly interesting thread.