Manny is a slur used to describe Portuguese in a derogatory way. Because it seems nine out of ten Portuguese guys are named "Manuel", or "Manny"
The word Manny is a racial slur that has been used historically to degrade and dehumanize portuguese. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to portuguese. If you are unsure about whether or not it is appropriate to use the word Manny, it is best to err on the side of caution and avoid using it in any situation.