What is the best way to ask a guy if he's bisexual?

In the most discrete way as possible.Instead of straight out asking him, what are some ways to edge into that topic without it looking like I eagerly want to know. Also it has to be a good way to ask him to get a truthful answer. B/c me being a guy, I know I wouldn't tell a guy I was bi if he asked me. Because I wouldn't know if he was bi. The downside in my head always outweighs the positive possibilities. The negative is that he would tell other people and that would suck.