By difficult do you mean reactive? A lot of ENFPs with strong Fi/Te have no problem telling you exactly how they feel if you cross one of their core values. I don't think ENFPs take well to a certain kind of hard teasing, either, we're too sensitive to people criticizing us...unless it's the sort of teasing that is playful, fun, and obviously intended without harm.
ENFPs I think are known for being pretty opinionated, but when we care about you we will let A LOT of things go...if I love you I'm going to try to analyze and rationalize your behavior, even if it offends or possibly hurts me sometimes, because I'm not gonna wanna judge you or do anything to lose you.
ENFPs have this strange way of "letting things go" and doing the live-and-let-live thing when it comes to how other people choose to live their lives, but also having this internal locus of control that will surprise the hell out of you if you dare to tread on our deeply held ethics or attempt to invade our personal space. There's also another paradox of us being Ne-dom playful and experimental and fairly free, and sometimes we're emotinally open to the point of allowing other people's energy and opinions to affect us far too much (that is, the opinions of people we are close to and care about, not people in general),but also I think we have this stable core of Te/Si that you may find will be rather stubborn and resistant to deviation from what we authentically are and truly want.
If you can live with and appreciate this sort of duality, the more mature ENFPs will tend to be extremely loyal to you.
Of course, sometimes very young or otherwise immature ENFPs can be infuriating or "difficult" if they're still exploring their world and trying to figure out who they are and what they want, because in that case you won't be able to pin us down, don't even try it. It was a mistake for anyone to attempt to contain me in any way until I was about 25 or 26 years old and had strongly developed my Fi, Te, and Si as well as my Ne, and knew who I am well enough to lose the fear of someone else trying to control me. I think once we have our 'core' built in a more mature manner, we fear committment less and less in terms of settling down. We've got to have that, though, otherwise we'll feel unsure of who we are and feel like we're being pulled in different directions and be deeply unhappy unless you let us do what we need to do i.e. go on our spiritual quest or whatever.