The idea that Vietnam veterans in the United States were spat on when they returned seems to have taken hold. It's mentioned in the movie First Blood (Rambo) and songs and in books, but there don't seem to be any first hand accounts of it.

In his book "The Spitting Image" Jerry Lembcke claims that it's a myth and never happened, or at least not in any confirmed incident. Furthermore it states that the peace movement were the vet's natural allies, rather than likely to spit on them.

What is the truth here?