Is there a good that may cause to experience negative marginal utility?

Question

For an individual consumer

Answer 1

Sure!

Let's say, for example, you're at a restaurant. You buy an entree, and it's excellent.

Then, you're still sort of hungry, so you order another plate of the same entree. It has diminished value (you're not as hungry), but still positive value.

Then, you decide that you want another plate. You eat the third plate, but now you've eaten so much that it makes you sick to your stomach. The third plate would have negative marginal utility - it made you sick and actually reduced the value of the entire meal, and may have cost you in other ways (taking a day off work, etc.

Another example is if there is a cost to dispose unwanted items - extra items become a liability since you don't want them, and actually have to pay to get rid of them.