What is the meaning of a 'no-brainer'?

Answer 1

It is something so obvious or so easy that you don't even need a brain to figure it out. Many people, however, incorrectly use the phrase to describe something that is almost completely opposite of its true meaning. To them, a no-brainer is something that is so obviously wrong that only someone without a brain could come up with it. In either case, the phrase is, of course, figurative. If you don't have a brain, you can't figure anything out, either rightly or wrongly, no matter how obvious or easy it is.