In introductory economics courses the concept of marginal utility is illustrated through simple examples like how much benefit one gets from eating another slice of pizza (i.e first slice provides 100 utils, second slice 50 etc).
I was wondering if there exists a utility function that can allow for the possibility of over consumption (i.e. a function that would produce -50 utils from the 10th slice of pizza ).
I know there would be issues with this since utility functions are only defined up to monotonic transformations, and concavity in our utility functions would violate the "averages preferred to extremes" assumption.
Does such a function exist?