There are many....
Springing to mind are the KD Greatcoat for ceremonial duties on Cyprus (in reality a brown storekeepers dust coat with brass buttons sown on) and the Warm Climate NBC Kit (with shorts). There is the oportunity to send the young erk to stores for a "Long Weight" - the SNCO asked them to sit "on that bench for a while" until they cottoned on.
However my favourite was the "mass spoof" of a course of baby pilots at Linton on Ouse many years ago. Their arrivals day programme was changed - at 0900 the course was at the main briefing room where they were met by the "doctor" wearing his white coat and stethoscope (in reality an air trafficer renowned for his practical japes). They were instructed to strip to their underwear and put on their flying helmets which had just been picked up from North Luffenham the previous week. The victims were told to wear the helmets for 15 minutes then their blood pressure was to be checked to ensure that the helmets were correctly fitted. Five minutes later, the Stn Cdr walked in to give his arrivals brief to the new young officers but instead found 12 nearly naked bodies as previously described. By all accounts he burst into uncontrollable laughter and left - at least his dignity was preserved.