They usually say that an unhealthy personality overuses its dominant function to the point of a loss of control, uses its secondary function poorly, leans too much on its tertiary, and stares its inferior function (worst nightmare) in the face, right?
In that case then it would be overblown Ne which is just that- flitting from one thing to another and going out of control with indecision, talking excessively and incoherently.
Poor Ti would explain the bad Ne - the head is obviously disorganized and failing to control behavior.
Excessive Fe would be appealing to people and acceptable behavior instead of finding the right way of doing things.
Finally the inferior Si would be a resigned confinement to the bare minimum, "easy" tedium.
In any case, some of the dark things my mind is capable of in times of stress are:
Becoming disillusioned with my beliefs. Essentially throwing away beliefs and escaping into new ones.
Becoming argumentative with people. Also dealing with arguments within my own mind. The rigid Ti and perceptive Ne always sees a flaw in an argument, so if I have two ideas that totally contradict each other, its likely that I won't be able to simply come to peace without an answer.
Running from commitments. Ne looks at everything as an experiment, when running wild has a tendency to tear up current projects at the mere idea of a better one.
Poor social intuition. Supplanting Fe for Ti has the result I think of meshing the two, making a poor analyst and a poor salesperson. Ti should be the proper guide to behavior, with Fe only as a side measure.
The proximity of Ti and Fe invites a danger, which is that I convince myself I am liked or have the capacity to be liked more than I think. A strong thinking type is not really a natural social butterfly. I may be able to provide good social cues and read quickly into people's behaviors, that's not the same as consistently developing relationships with people, which is made poor by low Si (I often forget people's names and act differently around them over time). And as Fe is overused it also invites things like possible reciprocal relationships (whether in love, friendship or business) which end up biting me in the ass. Then the Fe is expected even more from others and becomes exhausted, which will cause me to lose control with the person, and inevitably making me feel unlikable. Even worse, I will from there begin to consider myself stupid. Why? The tertiary Fe is essentially developed from Ne and Ti, so when Fe fails, Ti also has to take the fall. Then Ne looks for a new situation to feel happier, but with worse Ti and Fe, leading to the same cycle again with an even higher chance of failure. This goes on until Ti has the patience to analyze the past, present and future, discover the underlying mechanism behind all of this, how life might be continued without falling into the same trap.
The difference between dominant, secondary and tertiary Fe is the following: Dominant Fe is compulsive. Secondary Fe is committed. Tertiary Fe is instrumental. So an ESFJ is friendly out of compulsion, out of early developed or innate character. An INFJ is typically ideologically committed to serving good. An ENTP is only able to use FE like a tool, it's neither a matter of their character nor ideological commitment.