I've actually had sex with a guy before and enjoyed it no where near as much as I do with my GF. I like the penetration part, but I still need a woman there with me. A guy doesn't do it. The normal male aspects turn me off (deeper voice, rougher skin, etc) which is why after that, I am most definitely not gay or bi. It's not the want to have sex with a male, it's the want to have sex with a powerful, dominant female and to be dominated. Sorta like the female want to be with a guy who shows strength and protection and power. (This is just my opinion btw. I'm sure there are guys out there where the girl playing the guy role for them actually means they enjoy having sex with a male. There in being they're Bi. But for myself, that is not my preference. Through experience I might add.)

As for the girl perspective of it, I'm not exactly sure as I am not the girl but she tells me (and what I hear from others) is that the turn on is dominating a male and feeling the power from it.

And pansexual isn't the same as bisexual because you only see and are attracted to male and female as bisexual. Pansexual sees more than that.