This story is not quite "urban" but I know some of you have heard it before:
A soldier has been on patrol with his team during the Q Course/Ranger School/whatever... And is so exhausted he begins to hallucinate. The teams moves after a short security halt, only to do a head count and fnd him missing. They go back for him, and there he is, beating on a tree. The reason? He thinks it's a Coke machine that he has put money into, and it will neither give him his drink nor his money back.
I heard that story when I was in the Q Course in '82, and was quilty of telling it to my recruits when I was a Drill Sergeant in '98. Of course by then, the story had evolved so that the guy was in my class.
Well, the next time I heard he story was in 2000, at ANCOC (if you're thinking how in the hell did it take you 18 years to get to ANCOC?-I had a twelve year break in service) and the guy telling it had "witnessed" this while on patrol in PLDC.
Other persistent stories:
The private who ties himself to a buffer cord and chucks the buffer out a second story window, only to find the cord is too long, preventing him from killing himself.
The private who is thrown into a wall locker, and rolled down a flight of stairs while still inside it.
And my all time favorite, because it is just not possible:
(The others are, because privates are just that stupid)
If you remove the spade grips from the back of the M2, the recoil spring and guide rod will shoot out and impale you. "I've seen it happen. This one time, in ______, I saw one shoot out and put a hole in a cinder block wall/tin roof/jeep..."