When you find you have a tapeworm infestation after using the toilet. Instead of a normal lincoln logsets... you see a pile of bloody tapeworms with little poop nuggets that look like meatballs... thus, a spaghetti surprise.
My friend Matt just got back from Mexico and had to go to the hospital after having a spaghetti surprise in the toiler.
When a man dehydrates himself and receives oral sex. When he ejaculates in her (or his) mouth, the load is very thick, and spaghetti like, and the taste is very difficult to clear up by simply swallowing. The effect is maximized by ejaculating closer to the top of the tongue, but still in the mouth.
I drove for 14 hours straight yesterday. I didn't drink anything 'cause I didn't wanna have to stop and piss, so when my girlfriend got to suckin on my knob, she got quite the spaghetti surprise!