People who lie about having been in combat

Has everyone met someone who makes these claims with zero basis in fact?

I have encountered a few over the years. One that sticks out in my memory was a convict I met at the state prison in Walla Walla in the spring of 1988.

He told me his experiences in Vietnam messed him up and led to a series of bad decisions.

His sister subsequently told me he had not been in Vietnam.