Many years ago at an RAF base in South West Wales, the new course of students gathered in the groundschool. The "SMO" (one of the instructors from the squadron) told the students that they were to be part of a research programme investigating "Testicular Drop due to the effects of Excessive Gravity". The explanation given was that, as the course involved flights including prolonged high g manoeuvring, the RAF needed to know if it was having any effect on the family jewels. The programme would involve having their "amount of dangle" measured before and after the course so, if the first student could come to the front of the class and drop his trousers, "we'll get on with the measurement".
They fell for it and the first stude dropped his trousers and underpants and the "SMO" had the steel ruler next to his parts when the real SMO (female!!) burst through the doors with a camera!!