egg in (one's) beer
Something for nothing; a free, unnecessary, or unmerited bonus or favor. Most often used in the phrase, "What do you want, egg in your beer?" as a retort to someone who gripes or complains about something for which they should already be content. Your parents paid for your college degree and now you're moaning that they won't pay for your rent? What do you want, egg in your beer?
egg in your beer
A bonus, something for nothing, as in What do you want-egg in your beer? This expression dates from about 1940 and became widespread during World War II. The origin is unknown, since adding egg to beer does not improve the taste.