The etymology of the phrase comes from the idea of being force fed spaghetti, which resembles the tentacles, and the term breakfast which is sometimes used as a code word for sex. The breakfast thing really just indicates taking the noodles inside of yourself, normally in the case of eating, but in this case, not eating. People automatically realize that the phrase is not, in fact, referring to eating spaghetti for breakfast because of the unusual nature of such a meal.
Madam: My, I've never heard of that, what is it?
Waiter: Allow me to give you a free sample. BLURRRRGH! *sprouts tentacles*
Madam: AIEEEEEEEEEEEEEEEEEEE-- Ohh, yeah, deeper, to the left.