The term 'THEY'RE UNRETURNABLE' can be broken down into two parts: 'ACES' (4 letters) and 'UNRETURNABLE'. The word 'ACES' is a term used to describe something that is of the highest quality or excellence. It can also refer to playing cards with the highest value in a game. The word 'UNRETURNABLE' means that something cannot be returned or reversed. Together, the phrase 'THEY'RE UNRETURNABLE' implies that something is of the highest quality and cannot be reversed or undone.