Bikini state was removed a few years ago now and yes the weapons are loaded, but the magazine contains no rounds.
One of the posters hit the nail on the head earlier on, 'there are standards to maintain'.
Yes, what he did was funny for joe public, but when he is out there on duty, he is meant to be protecting Royalty. What if this were 10 Downing St or the White House and the guards/police starting doing pirouettes etc? They would look unprofessional and not remaining vigilant or alert.
He won't get sacked (military don't get 'sacked') but there are specific orders relating to guards and sentry's and he will be in the brown sticky stuff big time.
Admin Action, Military charge, Jankers (a form of punishment), Colchester is an option if a little extreme!
But I do think his hierarchy will be fuming as he has embarrassed his regiment by his actions.