Well, this is interesting. A few years ago I worked in kids' TV, and one afternoon one of our presenters said "can't be arsed" during a live broadcast. In the next cartoon break we hauled him out of the studio to give him a dressing down and he was absolutely baffled—he insisted he'd said "can't be asked", and claimed to have no idea that "can't be arsed" was even a thing. We still had to get him to apologise to the viewers, but those of us in the production team (who were a bit older than him) did wonder whether the phrase was changing among younger people.