pain in the ass; pain in the butt;

The phrases "pain in the ass" and "pain in the butt" are idiomatic expressions used colloquially to describe someone or something that is extremely irritating or bothersome. The use of the word "pain" implies that dealing with the person or situation consistently causes frustration, annoyance, or difficulty, much like the discomfort caused by physical pain. It is a metaphorical expression commonly used in informal settings to convey a strong negative sentiment towards someone or something.