What is the origin of the idiom "chopped liver" and when to use it?

The idiom "chopped liver" has Jewish origins and is commonly used in American English. It originates from a traditional Jewish dish called "gribenes," which consists of crispy bits of chicken or goose skin and onions that are often considered a delicacy. However, "gribenes" is not as highly regarded as chopped liver in Jewish cuisine, and thus the expression "What am I, chopped liver?" developed. This idiom is used to express feelings of being overlooked, unimportant, or undervalued, comparing oneself to something less significant.