I have had sex with "straight" men on occasion. First experience was freshman year of college when out hiking, my friend and I went skinny dipping. One thing led to another and it happened. We were caught by a few women in the group we were in. The said it looked really hot to watch two tall, well built golden gods going at it. It has always been a one time thing and is always serendipitous. I always thought there was something about me that provoked these sex-capades.
I also believe everyone is bisexual to some degree, but do not acknowledge it or act upon it because of religious reasons or social mores.