Flirting is not sexy. And flirting with a lot of people is disgusting.
I disagree that flirting with many people is disgusting, but I have been told this by other types before, especially other Is.
My INFJ friend asked me to explain it to her once, and I don't entirely know how--it's just been a natural and somewhat involuntary part of the way I interact with many people. It's something used to do when I was much younger without even thinking about it. Now at least I do it by choice! I typically only flirt if I genuinely like someone and want to know more about him/her, and I typically don't turn on the charm if it's not sincere. I don't mean for it to be misleading, although I know sometimes it is.
I do agree that flirting is not necessarily sexy and doesn't necessarily make someone sexy . . . but it definitely CAN be sexy. I think a lot of E-types interact with people this way (I know a couple of ENTPs and ENTJs who are very flirtatious as well), but I think ENFPs also tend to be colorful in the way they dress and to have vibrant or exuberant personas when they are interacting with others. All of these things combine, I think, to make the ENFP personality type a sexy and attractive one.