I'll just chip in and say i agree for the most part with what the other ENTP's are saying, and also what's been said about us, generally.
To emphasize though:
It's not fake - it's quintessentially who I am, to be that way - whatever way the situation requires. Because my primary interest is in improving things - anything - it's satisfying the deepest parts of myself to be able to become the means of improvement.
It's not done in order to deceive anyone; I'm not deceiving anyone because I'm still always myself, just played on different 'wavelengths'. For me it's kinda like just a deeper extension of speaking Spanish for the benefit of a person who only speaks Spanish - to speak English wouldn't be "being myself" just because it's my first language, but it'd just be foolish and a severe impediment to effective communication. When I'm with a person, I'm basically on the lookout for signs of what 'social language' they speak, and translating my true inner self into whatever that language is, to the best of my ability.
The aim is not just to make a point, but for me, to enable that person and myself to get to know each other quickest, best, and with the fewest misunderstandings. I believe it increases both harmony and efficiency, and experience bears that out.
edit - I will also add that my ENFP brother is able to get along in any situation and with 99% of people, but I think the fundamental difference between how he does it and how I do it is that I can literally come across as a totally different person, whilst he finds a way to be the same person anywhere, and make it work. He doesn't change his presentation much at all, but somehow finds a way to do it so that people like him anyway. For me, the main point isn't necessarily that they like me, but that they understand me and I them.