The Queen's guards are notorious for keeping a straight face, regardless of what pesty tourists throw at them.
However, it seems a Scotsman guarding St James' Palace simply had enough.
A man in a grey coat got the fright of his life while dancing and singing in front of the guard and his colleague.
He steps forward smartly, stamping his feet and shouting: "Halt! Get yourself away!"
The tourist turned around, stunned, before scampering away as the Scotsman kept shouting at him to turn the camera off.