Definition of "flirting" (dictionary.com):
(1) To make playfully romantic or sexual overtures.
(2) To deal playfully, triflingly, or superficially with.
I'm an INTJ and I personally have to say that flirting (defined as above, especially definition (1)), is truly a disgusting way to live your life. It may be in an ENFP's nature to flirt with people, but you lead people on and eventually you hurt them in a way that is unforgivable. I know I sound harsh, but what can I say, this is how I see it. You ENFP's are attention whores and without any sense of stability or conviction in your life. Once your interest in a person has died, you find someone else and flirt with them. How are others supposed to trust you, especially in a relationship. I'm very bitter.
A few months ago, I met this girl who was an ENFP. I thought she was pretty, but like most people in the world, I didn't really talk to her (b/c of my INTJness). Initially, I didn't like her personality. She seemed to want to please everyone in the world. But as time passed, I found her to be seemingly warm and caring, and she grew on me, she somehow broke my barrier. I am a really shy person to be honest. Nonetheless, I began to let myself out, I told her about things I don't tell most people in the world. She seemed to care about what I had to say, so I told her more things (stuff I've never told anyone), my dreams, my fears, hopes, etc...I trusted her. And trust me, breaking an INTJ's barrier isn't easy, especially if he initially doesn't like your personality. I thought that she was genuinely interested in me, and sometimes it seemed that she was able to remember all the little things I did, so I assumed that she noticed those things because of her romantic interest in me. Other times, she would find me and talk with me, alone.
So, I gathered all my courage, which for me took great amounts of energy and focus. I strategically found the perfect time and place, and I told her my feelings. And that was when I was surprised to hear that she only wanted to be my "friend", that she didn't see me that way. Maybe, for an ENFP, leading someone on is a hobby, but that really hurt. I felt so betrayed. It's been several weeks now, and I still feel so worthless, so used, and even more isolated in my life than I've ever been. It's so hard for me to open up to anyone now. I feel that people are just waiting to stab me in the back. I feel like a fool for falling for her flirtatious behavior. I should have seen through it, but now all I can think about is how much I cared for that whore. As an INTJ, I hate to admit it, but I cried (not in front of her, of course). It had been so many years since the last time I cried.
If this doesn't show you why you shouldn't flirt with someone (unless you're genuinely interested in them and need some way to approach them), then you ENFP's aren't warm and caring, but rather heartless monsters preying on other's weaknesses to make yourselves feel better.