"You're about as useful as a one-legged man at an arse kicking contest"

This quote is an amusing way of saying that somebody is not extremely useful. It indicates that the person is so worthless that they would not have the ability to contribute anything to a situation, even if it was something as simple as an arse kicking contest. The quote is also a way of highlighting the absurdity of the circumstance, as a one-legged male would certainly not be able to take part in such a contest. The quote is likewise a method of buffooning the individual being referred to, as it implies that they are so useless that they are not even as helpful as a one-legged guy. The quote is a humorous method of expressing the speaker's opinion that the individual being described is not really useful.