like comparing apples and oranges

Highlighting the similarities and differences between two people or things that are not really comparable at all. You can't compare your job as a nurse to mine as an engineer—that's like comparing apples and oranges! Look, comparing the business model of a small local business to that of a giant global conglomerate is like comparing apples and oranges—they are two completely different things!

See also: and, apple, compare, like, orange

apples and oranges, like comparing

Comparing two unlike objects or issues. This term, dating from the second half of the 1900s, has largely replaced the difference between chalk and cheese, at least in America. The latter expression of disparateness is much older, dating from the 1500s. Why apples and oranges, since they’re both fruits, and not some other object is unclear. Nevertheless, it has caught on and is on the way to being a cliché.