Ha, hop in the tub with Mr. Bubble indeed!
I vaguely recall having some kind of bubble bath around when I was a kid, and having to rinse off after using it. I think the point of such things is to give kids a reason to want to get in the tub, which some of 'em might otherwise resist.
If you get nostalgic for things that will grow all manner of blue fuzz, you can always take a hunk of bread or a roll, and stick it in the soap dish, and wait 'til the fuzzy blue mould starts to grow all over it... (eewww!)
/me ducks & runs!