My informant told me this joke as we were commenting on jokes in bad taste, such as racist jokes and dead baby jokes.

How many Vietnam vets does it take to screw in a light bulb?

YOU DON’T KNOW MAN, YOU WEREN’T THERE!

She thought it was funny because it plays off of the stereotype of the PTSD Vietnam soldier who overreacts to the slightest thing.  She says that people love stereotypes, even if they know they aren’t true.

This joke takes a known form of a joke “How many x does it take to screw in a light bulb?” and throws in the vetern sterotype.  This form is very easy to make blason poulaire out of because it relys on puns and stereotypes as the punchline.  It is also a way to cope with the difficult issue of the Vietnam war.  The punchline is a quote from Jacob’s Ladder, a thriller about a Vietnam war veteran made in 1990.  The movie is about a traumatized vet who finds out that his post-war life isn’t what he believes it to be when he’s attacked by  horned creatures in the subway and his dead son comes to visit him*

*Jacob’s ladder: http://www.imdb.com/title/tt0099871/