Leah asked, and in case anyone was wondering...
Stink Pink is a rhyming game. You think of two words that rhyme, and the others try to guess your words. You give them two clues:
1. Syllables, and
Okay, so I'm thinking of two words that rhyme. They each have one syllable, so I say Stink Pink. (If they had two syllables each, they would be a Stinky Pinky; three is a Stinkety Pinkety, and so on.) Then I throw out my synonyms: Naked Cowboy.
The answer - of course - is nude dude.
Try this one.
Stinky Pinky, flexible wood.
Or, Stinky Pinky, excitable musician.
The words don't have to go together at all. They just have to rhyme. But it's more funny if they do sort of go together. And you can throw in another level of complexity by using homonyms. You know... Stink Pink, a serious tomb is a grave grave.
Of course they boys tend to go for refined and subtle humor, like Gunnar's piece de resistance last night, Stink Pink, sour methane. (Just think like an 8 year old boy, you'll get it.)
But I put up with it because - hey - once again, they're expanding their vocabularies and it's a stress-free way to sneak in some grammar (syllables, synonyms, homonyms, antonyms, etc.) as well.
UPDATE - answers in the comments.