A guy is totally straight when he is completely, 100%, definitely not gay. This is the kind of guy who will let you know, at every opportunity that he isn't gay... very not gay. Boy is this guy not gay. Hey, did you ever hear him tell you about the time he was totally having sex with this chick? This guy is NOT GAY... just ask him... or don't, he'll tell you anyway.
"Man, I'm so totally straight. I would never have sex with a dude, I have sex with women! Did I mention that I'm straight?"