It's not social protocol. Try to get away from all of that stuff for a second, and just look at the terms Introverted and Extroverted.
Do you convey moods, influence from other people's emotional standpoint, generate liveliness (even in a subdued way), build any kind of overt, inviting displays in your behavior? Fe. Are you feelings a little more internal, under the surface and do you try to make more personal connections first? Fi.
That said, even if you aren't a feeler, and don't do either of those "well", the quadras are still broken down where even Ti or Te types value one of the F styles more.
Beta ESTps and ISTjs appreciate the INFp and ENFj Fe. No matter what, the entire quadra is given to a lot of boisterousness, theatricality, outward expressions, louder type of social situations, etc..
Alpha T types like ENTp and INTj aren't good at creating emotional situations themselves (although ENTps do reach out.. and indirectly need attention), but they appreciate their ESFj and ISFp friends who are more playful and relaxed.. the kind of people who create a lot of cozy Si-Fe parties or social situations. The Alpha quadra in general is lighthearted, likes some goofyness and laughter, group projects, and talking about pointless theorizing and movie tastes and art, and Ts appreciate a hug every once in awhile, etc..
Deltas and Gammas are different than Alpha and Beta for being more Fi valuing..
In the case of Deltas, their Fi is very philosophical and idealistic.. it seeks to make more serious close F connections in that manner. T types like ISTps, for example, generally don't loosen up in places where too many Betas or Alphas are (Fe), but they appreciate the closer, more in depth Fi connections that INFjs and ENFps bring up. The whole quadra has a certain air of quiet wisdom about it, be it F or T, is generally laid back, democratic, not overly excited, and yet practical in many ways too..
Gammas are a little more materialistic, Fi, but with more of an emphasis with Se.. the connections are serious in the sense that discussions may revolve more around career goals (Ni), or how to enact them (Te) (not that that has anything do with traditionalism though). Groups are generally smaller than other quadra groups (possibly because of that Se-Fi.. it's restricts more involvement without good reason. Sometimes there's a lot of "us vs them" mentality going on).
Anyways, I'm not even typed at the moment, so I have no place to talk. Just trying to point out that the difference between Fe/Fi is not as simple as "PC-ness".