The phrase 'rear-end foremost' refers to something that is done or placed in a way that is opposite to the usual or natural order. Synonyms for this phrase include 'backwards,' 'inverted,' 'reversed,' 'upside-down,' and 'inside-out.' These words are often used to describe situations where something is turned around or flipped over, such as a car accident where one vehicle hits another from behind. They can also be used metaphorically to describe situations where someone is doing something in an unconventional or unexpected way, or when something is done in a way that is contrary to the norm.