Guppie is a slur used to describe Greeks in a derogatory way. Pronounced 'guppy' (like the fish). From Greek + Yuppie. Originated in Astoria, New York, which is densely populated with Greeks. Not necessarily derogatory.
The word Guppie is a racial slur that has been used historically to degrade and dehumanize greeks. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to greeks. If you are unsure about whether or not it is appropriate to use the word Guppie, it is best to err on the side of caution and avoid using it in any situation.