I think you should talk about how to calculate how far back you have to start BEHIND the RN/RNR/RM/RMR/Sea Scouts when on parade because of the difference in marching pace. And of course you can always point out that the crabs have to start 50 yards to the left given their marching style. It always goes down a storm in mixed company.
It also gives plenty of scope to discuss all the foreigner sterotypes eg. Italians marching backwards, Germans marching into Austria no matter where they start, Americans unable to march without a 3-month shock and awe bombing campaign first etc. etc. etc.