I've been reading up on them, and they actually sound kind of cool.
ESFJs’ Fe can present differently among strangers than it does with their intimates. In larger groups, ESFJs may seem consistently “positive” in their expressions as part of their attempt to cultivate good social feelings. In the company of close confidants, however, they are more apt to share their negative emotions and grievances. And because their words are often bathed in emotion, ESFJs can seem intense or dramatic in their expressions. While such expressions are commonly interpreted as “irrational” by Thinkers or Fi types, they are rational to the degree to which they accurately reflect the nature of the experienced emotion. In many instances, given sufficient time, ESFJs will further refine or soften their initial Fe judgments as they move through the Perceiving functions of their functional stack.In contrast to IFPs, ESFJs can have a more difficult time independently perceiving their own emotions. This is due to the fact that their Feeling function is extraverted rather than introverted. Consequently, ESFJs don’t spend as much time trying to independently sort out their emotions. Inwardly, they deal largely in the currency of Si. So when ESFJs find themselves in emotionally troubling circumstances, they often (and should) turn to others for support or guidance. Expressing themselves through their Fe is critical to their psychological (and physical) health and well-being. Even if doing so does not provide them with an immediate solution to the problem at hand, they tend to feel better once they have expressed their feelings, be it through words or through tears. Unfortunately, parents and teachers often fail to understand this about their FJ children and may end up stifling their Fe expressions. At least in the U.S., Fi seems to be the most common and socially accepted way to handle emotions. ESFJ females, in particular, can feel misunderstood in a culture predominated by FP and TJ females.
So despite the positive emotional output much of the time, they can and do express more negative emotions, just not among people who aren't in their inner circle. I don't see that as being fake, I see that as being practical, especially when you have types that are always "absorbing" the vibes of others around. And what is an inner circle for if you aren't supposed to share the stuff you're afraid to talk about anyone else with? What's so bad about that?
To me it seems like an ESFJ wouldn't do the "I'm mad at you because you splashed too much water in the sink, even though I'm really mad about something else that I won't tell you" thing. Would that be correct? If you were close to an ESFJ, they probably wouldn't need much pushing or wait until an argument to tell you what was bothering them, it seems. To me, that's good. I wish I was better at that.
It's also interesting to contrast the dominant Extraverted Feeling dynamc with the inferior Extraverted Feeling. More on that if people are interested.