Movie fact: The movie Full Metal Jacket is often cited as required viewing for people about to enter the Marine Corps to see what Basic Training is like, due in no small part to the fact that the actor who plays the lead Drill Instructor, R. Lee Ermey, actually was a Marine Corps Drill Instructor during the Vietnam era. In addition to his role, he served as a Technical Advisor, and also had a hand in building the set, how the barracks looked, and was the only person on set permitted by the director to ad-lib his lines. In fact, all the insults he spouts off at the recruits, he made up literally on the spot, and every take, he would spout off a different insult, eventually making up several pages' worth of one-line insults to spew at the recruits. His training video on ad-libbing involved him yelling insults at a group of British Royal Marines in formation, all while being pelted with oranges. During the whole 10-minute tirade, he never flinched, ducked, or repeated himself, and several of the Royal Marines later reported they were legitimately terrified of him. People were so used to him giving orders that in one instance, he was talking to director Stanley Kubrick, who was sitting down, and Ermey barked an order to stand up when being spoken to. Almost instinctively, Kubrick stood at attention and listened to Ermey before realizing what happened.
Also, even after breaking all the ribs on his left side due to an accident in a Jeep, GySgt. Ermey continued filming without taking any leave.