Rather like p***ing off the Regimental Sergeant Major. There's an apocryphal story of a young private on parade. The RSM walks up to him and, seeing he's a rather scruffy and disorganised individual, jabs him with his pace stick and yells, "Soldier, there's an idiot at the end of this pace stick" and the soldier replies, "Well he's not at this end, Sarn't Major." Cue explosive SNCO and one young private who spent a lot of time cleaning the latrines with the much-vaunted 4-haired toothbrush!