up one's own ass

The idiom "up one's own ass" is a vulgar expression used to describe someone who is excessively self-centered, arrogant, or self-absorbed. It originated in American English during the late 20th century as a more explicit variant of the expression "up one's own behind," which had a similar meaning of being overly focused on oneself. The usage of "ass" in the idiom adds a stronger emphasis on vulgarity and contempt.

It is important to note that this idiom should not be taken literally. Instead, it is a figurative expression used for comedic effect, insult, or criticism. The idiom implies that the person in question is so self-absorbed that they are oblivious to the needs, perspectives, or criticisms of others.

The idiomatic phrase is primarily used in spoken language and informal writing, and is typically avoided in polite conversation or formal contexts due to its crude nature. Its offensive nature makes it unsuitable for publication in mainstream media outlets and it is generally considered inappropriate in professional settings.

The final related idiom is "toot one's own horn". This idiom means to brag or boast about one's own achievements or abilities. It is similar to "up one's own ass" in the sense that it implies a certain level of self-centeredness or arrogance. However, "toot one's own horn" focuses specifically on self-promotion rather than a general sense of self-absorption.