I think the Kinsey scale thing is pretty much on point. There are people out there who I think are 100% straight (or least 99.9%) but I think those people are actually in the minority. I think everyone has some kind of attraction or curiosity to the same sex, just at different levels of intensity.
I think there are guys who are "straight", meaning that they are mostly attracted to women and don't typically seek out men or check out other guys. However, if they're horny enough and the opportunity presents itself (drunk, etc.) they'll maybe fool around with a male friend or something. I don't think that necessarily makes them "gay", because under normal circumstances they probably wouldn't be pursuing other men.
I think what really classifies someone as gay, straight, or bisexual is more of an emotional thing than a physical thing. Whoever you try to pursue intimate relationships with and feel that emotional connection with is probably what you can "label" your sexuality as, if you feel the need to. I don't think if a man who normally only dates/has sex with women, ends up fooling around with a guy a couple times in his life just for the heck of it, automatically should be labeled as "gay".
Whatever, that's just me opinion though. Sexuality is very complex, and it's almost like everyone has their own "DNA" (no two people have the same exact sexuality), or at least that's how I think of it. It's not all black and white. There are many shades of gray.
Unfortunately, because homosexuality is so frowned upon in society, I think most people (especially men who identify as "straight") suppress their homosexual thoughts/feelings and never explore them in fear of being judged by their friends, family, and peers. For some reason, I also think guys who identify as straight think it makes them less manly or masculine if they find another guy attractive. Which is why I hate it when guys say "no homo" after making a comment about something that could be perceived as "gay". Girls are always commenting on how other girls are so pretty, and you don't hear them saying "no homo". Why can't guys be the same way?