I always looked at it this way:
People who use Fi will be interested in consistency. They will avoid changing the way they act for the sake of others. Thus, they will try to find a way to still be themselves, but also keep harmony in a group setting (unless someone does something that opposes their personal values, in which case they are likely to be hurt or made uncomfortable). People with strong Fi don't like to compromise their consistency. They also never let themselves forget where they stand on something. They know who they are, and have a good sense of who the people around them are. They'd be more comfortable with really good friendships where they know the person really well, as opposed to having several acquaintences, which is more typical of someone who uses Fe strongly.
Fe is all about being appropriate. People with strong Fe will adapt to social situations based on the vibe of the group dynamic; or the unspoken rules. Fe's will try not to offend anyone, and like to make everyone feel comfortable. It's like we get into a character almost. We're still being ourselves, but we're showing different sides of ourselves to different people, and hiding sides that we sense the other people in the group either wouldn't apprciate, or wouldn't be interested in. Where Fi's are usually good at knowing people's motivations and emotional states, Fe's are good at picking up on the values of the group or individual of interest, and use that to find the right words. It's like Fi asks "do I feel like I can trust you?" and Fe asks "do you feel like you can trust me?"
For example, my sister is an INFP. Since she uses Fi and Ne, she is always talking about a lot of different things in conversation. Some things she says aren't quite relevant, and she sometimes talks about things that other people in the group don't really find all that interesting. This usually means that she gets the attention of one or two people, and they end up in their own conversation, which she likes, because she likes to get to know people one on one and get a feel for them. She'll pick up on who she can and cannot trust, and avoid those people that rub her the wrong way. She also doesn't like to be all give; she needs someone to show they care about her too. If she knows a relationship won't work out, she isn't going to try to make it. Fi's don't want to waste their time with meaningless relationships; they want to build deeper ones.
For me, on the other hand, I like to make sure I'm not leaving anybody out of the conversation. I'll try to keep everything within common interest, and be sure not to say anything too irrelevant or that has the potential to come across differently than I intended. Fe's tend to be extremely careful with words. Fi's can be, too, but they tend to talk more about personal interest than group interest. My sister often wonders why I act differently with certain people, or why I didn't bring up a certain topic in conversation. Fe's often run the risk of coming across as hypocritical, because they aren't a consistent in their communication style as Fi's, and Fi's usually pick up on inconsistently very easily. Fe's are fine with giving more than they're getting back. Mind you, this means that we tend to have more acquaintences and friendly conversations that don't really lead to much more than that, but we're OK with that to some degree. With the true friends we have, that's quite a different story...
