Or when one’s poop is very very oily?
Eating Olestra?
A good reason for consulting a real doctor.
I have a child with cystic fibrosis, and one of the things I watch for is oily poop (means he probably needs more of a medicine he takes).
But that’s only one condition - I’m sure there are other, far less rare conditions that cause oily poop - and your question is pretty vague. (For example, who is suffering oily poop? You? An infant? Did it start suddenly? Questions abound.)
I think you need a doctor’s opinion, not ours.
Have you recently had escolar, or “super white tuna”? It’s a tasty fish which has relatively recently become popular… the only problem is that the oil in it is undigestable, so you end up with oily poop. That’s why it’s called the “ExLax Fish”.
A shame, 'cause it is very tasty.
Escolar and Oilfish (which have a similar effect) are sold under a bewildering variety of names, including super white albacore, ivory tuna, walu, butterfish, and African bluenose.
I’m not a doctor, but the condition you describe sounds like steatorrhea, see Wikipedia here: Steatorrhea - Wikipedia. It’s probably just because of something you ate, but could indicate something worse. It’s sufficiently weird that I think I’d probably run off (no pun intended) to see a doctor.
Well, considering the effects, the name “butterfish” makes a lot of sense. 
It’s steatorrhea, or oily stools. There are many potential causes, CF being but one of them.
It’s usually a sign of inadequate lipase (the enzyme needed to break down fats) or excess dietary oil. Sometimes it occurs when non-digestible oils (like mineral oil) are ingested.
It’s often a sign of dietary oil excess and needn’t represent a disease process.
Consult a live physician in person if there are concerns.
Oh yeah, steatorrhea makes for some really horribly smelly stools. All the volatile short-chain oils that are produced from the oil by the bacteria in the gut are malignantly aromatic.
Now that’s a phrase I don’t see used nearly enough.
How about the classic description of a gallstone patient?
“Forty-ish fecund flatulent female with foul, frothy, floating feces”
::shudder:: I’d heard the first four fs but the second quartet is new to me.
Oh, I know that one! It’s from Shakepeare, isn’t it?
Nope, sounds like Grendel’s mom to me…
I love medical questions on the SDMB.
The medical-question poster usually provides 1/10 (on a good day) of the information as someone who is trying to figure out why their 1997 Dodge Dakota has a vibration from the left rear wheel area; only between 45-55mph; only on Sundays in May; and only after dropping the mother-in-law off. Odometer readings; the condition of the engine oil; and even the size/name/aspect ratio of the tires might be included. Sometimes we know the car’s color.
But when posting a question about someone’s* health*, all we get is “Hey, my shit’s greasy.”
.
Well, we do discourage questions seeking medical advice. If the OP had given out information of the sort you’d give to a physician when seeking diagnosis or treatment, the thread would probably have been closed.
Gfactor
General Questions Moderator
Hey, I just had some escolar last week, in St. Pete Beach! The waitress failed to mention that particular effect, and I didn’t notice anything out of the ordinary since. For what is worth the fish was delicious.
So we can just take stabs in the dark because someone is doing a terrible job of seeking what might be a diagnosis? 
If they do a good job, the thread is closed.
QtM did a nice job of explaining the causes in question. All without the details. He didn’t make a medical diagnosis. If we need to start asking a bunch of follow-up questions about a specific condition, it’s probably time to close the thread. This isn’t the place for making differential diagnoses. It’s a forum called General Questions, where you can ask general questions about things. There is some crossover, to be sure. That’s one of the reasons we don’t issue warnings for that sort of thing. But that’s how it works.
Here is the rule:
Factual Questions Rules & FAQs - Factual Questions - Straight Dope Message Board
I agree it seems ironic, but that’s how it works.
Did you go to the Fourth of July celebration in Point State Park too? Mr. Neville said the greasy food we got there upset his stomach. I suppose the food at similar celebrations also tends toward the greasy side.
Is there a chance these oily poops are going to catch on fire?