I knew quite a few folk who had served in Vietnam. Most were, at least ostensibly, reasonably well adjusted, functional human beings. There was perhaps a minority (but still a statistical over-representation) of vaguely functional dipsomaniacs as well.
We had one ex-Vietnam Warrant Officer, who, when drink had been taken, would invariably resort to his two party pieces. The first was emptying and then eating a 2 pint glass beer jug. The second was flopping his tackle out and placing it on the shoulders of unsuspecting soldiery. Equal opportunity offender our man, happy to play that trick on male and female soldiers. IIRC it was that finally did for him, although that may be be wishful thinking. Whether that was a result of his service in Vietnam or whether he was just an obnoxious ass to start with, it was impossible to say.