The Spanish thing with 5 is a lewd rhyme as well. A pretty tortured one, too. It refers to anal sex, but the word they're rhyming isn't butt. Or sex. It's just a less common word for sticking a thing into a thing.

I don't know what the 33 thing is about, though.

I looked it up, apparently there's a saying where people say "my balls 33" to mean that something is false or not gonna happen? Even people who know the expression seem confused about where it came from. I don't know, your guess is as good as mine here.