The pizza = sex connection is happening since the 90s everywhere, check this episode of one piece for example, what happens after pizza is mentioned at the very end of the episode last 5 min http://www.animeid.tv/v/one-piece-625

As far as I'm aware, the only codewords we have verified are (1) that "cheese pizza" is code for child pornography (via urbandictionary, for example, but this is common knowledge on the dark web, 4chan, etc), and hence "pizza" could be an adaptation of that, and (2) "cheese" is sometimes slang for a female (also via urbandictionary). People on 4chan claimed other codewords (hotdog, pasta, sauce) appeared in informal dictionaries, but I have yet to see a source for those.

Removing this post per rule 4.