Many people in my extended family are ENTPs, and I do find them intimidating. They're all scary brilliant and mercurial -- they know what they want, they go for it, and they're often ruthless. Manipulative, too, because they know enough about people to twist them around to get what they want. Young, immature ENTPs are especially dangerous. Often prodigious, they are very good at getting their own way. In my experience they've been uncaring as to how they've gone about doing it.
I call them the "dying baby joke" crowd.
Maybe I find them disconcerting because they are similar to me in a lot of ways. The whole shared Ne, I guess. But unless I am super-passionate about something, it's tough for me to maintain a dispassionate logical intensity. I also find it very hard to assert myself at the expense of others. I find it easier to hide whatever knowledge I have behind a laidback, goofy exterior. My relatives are always high-intensity and guard their emotional cores so well, it's impossible for outsiders to gauge what they feel or think. I feel sometimes that they live in a different, almost superhuman existence that I can't quite understand, because they've made themselves so ambiguous to me. And, of course, I always feel disrespected in our conversations, so I ignore them.
I do know two ENTPs as friends, and because they respect me, we get on very well. Respect is the key factor. In my experience, if I haven't earned the unconditional respect of an ENTP, it's not worth engaging.