This is British slang and is a slightly less vulgar way of saying pain in the arse or pain in the ass if you are American. In this expression the bum in question isn’t an American bum, a word that dates from around the mid nineteenth century, but an English or Australian bum, a word that dates back to the early seventeenth century. At one time the word was not considered to be vulgar at all and was used extensively during the seventeenth an eighteenth centuries. One Gentleman Soldier, fighting for the King during the English Civil War, wrote in a letter that on one occasion the going as so difficult that he “slipped and fell on my bum”.
by AKACroatalin March 4, 2019
Pain in the bum is a British slang equivalent of pain in the ass. The bum in this case isn't an American bum, but a English bum which is a slightly less vulgar equivalent of arse, or if you are American ass. At one time, certainly during during the seventeenth century the word bum wasn't considered vulgar at all, one Gentleman Soldier, fighting for the King during the English Civil War, recorded how on one occasion the going was so difficult that he "slipped and fell on my bum".
by Croatalin January 16, 2014
by STOCKHOLM-SYNDROME-4-THE-DEVIL May 10, 2022