A rhetorical question used by a person who feels they are being given less attention or consideration than someone else.
One of two explanations exist for how this expression came to be. The first is, liver is sometimes not as appreciated as much as other foods, and is often discarded in favor of something more desirable.
The second explanation, Wikipedia says, is that chopped liver is served as a side dish in some places, and not a main dish. Hence, someone who has an opinion and feels it's not being considered as important as someone else's might feel as thought they are being treated like a side dish.
The phrase is used in a comic strip from the Ames Daily Tribune newspaper, 1971. The comic is called Winthrop, written by Dick Cavalli, who later discontinued it:
* Jake asked Chell and myself what we thought of his new hat, but he seemed to ignore my comments... what am I, chopped liver?
Find more sayings with this handy list of phrases. It has their meanings and other interesting information!
knowyourphrase.com - Meanings and Origins of Phrases and Idioms
Note: Have you ever tried finding something with your eyes closed? It'd probably be pretty tough, or impossible. Well, that's sorta how the origins for phrases are. A lot of the time, the origins of phrases are totally unclear! What is listed are the plausible theories that most people agree on, for how a saying originated, but it may not always be a for sure thing!
As for the quotes, they are to be used as an indicator for the reader to help them determine how far back in history these expressions go. The quotes are the oldest written forms that I could find from books, newspapers, poems, and so on, but keep in mind there's a good chance of an older recording existing and I just missed it. If you know of any older recordings that are further back than mine, go ahead and inform me! If, you know, you want to.
Phrases and Idioms
There are claims that this exact expression appears earlier in the 1940s or 1950s, but the oldest written form I could find is from the newspaper above.