Two nuns decide they're going to sneak out of the convent and have a real
night on the town.  They hit all the bars and dance clubs, and decide
they've finally got to head back to the convent.

To enter the convent's grounds they have to crawl under some barbed wire.
The nuns start crawling under the wire on their bellies.

As they're crawling under the wire, the first nun turns to the second and
says, "I feel like a Marine."

The second replies, "Yeah, me too, but where can you find one this time of 
night?"