One day, a Marine Gunnery Sergeant was invited to dine with his Commander in the field mess.
When they entered the mess area they found the place quite crowded.
They finally noticed a table with two empty chairs. There were three lieutenants seated there, so the Colonel asked if they might join them. The lieutenants, of course, promptly invited them to join the table. The Colonel and the Gunny ordered lunch and engaged in light conversation as they ate.
At one point the Gunny mentioned that he had observed characteristics about many officers from which he could normally determine the sources of their commissioning. The lieutenants were eager to hear about this and asked if he could tell how each of them had been commissioned.
The Gunny turned to the lieutenant on his left and said that the he had received his commission through attendance at ROTC. The young officer confirmed that this was indeed correct and asked how the Gunny had figured determined this. The Gunny replied that by his conversation the lieutenant seemed to have a strong academic background but limited military experience.
The Gunny then told the lieutenant on his right that he had gone through OCS after previously serving as an enlisted man. The lieutenant confirmed that was indeed the case, and asked how the Gunny had figured it out. The Gunny replied that the lieutenant's conversation indicated that he had a firm military background and a lot of common sense, but not much book learning.
At this, the third lieutenant asked the Gunny if he had determined how he had received his commission. The Gunny promptly replied that the lieutenant had graduated from the United States Naval Academy. The young officer stated that this was correct and asked if the Gunny had noticed his high level of intelligence, precise military bearing, or other superior qualities acquired at the Naval Academy. The Gunny replied that it was none of these that had tipped him off, he merely observed the lieutenant's class ring while he was picking his nose.