There's one problem with this story: there's no way that old Marine said “crap”!
Personnel Manager: "What is your greatest weakness ?"
Old Marine: "Honesty"
Personnel Manager: "I don't think honesty is a weakness !"
Old Marine: "I don't give a crap what you think"
I've hired a few ex-Marines, and the interviews I had with some of them rank as both the most interesting and most entertaining I've ever had. This reads as entirely plausible to me :)