Something that irritates you very much or makes you angry. It is especially used with something that would test one's patience. That is the English version. The American version would be a 'pain in the ass'. Tha 'arse or ass is the buttocks or rear end. A more polite way to say it is a 'pain in the neck'. "We have to fill out all these forms just to sign up for school. This will take hours! What a pain in the arse!" "He's been complaining ever since we started out on this trip. He's a real pain in the arse."

Arse is slang for ass or butt. "A pain in the ass" is an expression which means something is really difficult or troublesome. A person can be a pain in the arse, a job can be a pain in the arse, anything can be a pain in the ass if it is difficult or it causes you problems. For a person, a pain in the ass is the same as a jerk. My boss is making me work on Saturday, what a pain in the ass/arse. I can't open this coconut, what a pain in the ass/arse.

"It is annoying." or "It is difficult." - "pain in the arse" is very informal slang. "arse" is British English "ass" is American English ... meaning the buttocks or anus.

Whoever said that to you should be ashamed hehehehe