In this post, Dan Ray notes that the word "Jew" may be offensive but "only from the outside". I can think of many other examples of terms that are neutral (or even affectionate) if spoken by individuals within a group, but are offensive or derogatory if spoken by someone outside of the group.
Is there a term describing such a word?
Note, I am not asking why this phenomenon exists, only if there is a word for it.
I think these are called "reclaimed words" or "reappropriated words":
Reappropriation or reclamation is the cultural process by which a group reclaims terms or artifacts that were previously used in a way disparaging of that group.
This is often the case for derogatory terms - they are co-opted by the groups and thereby defused within the group. From searching, I don't think there is a different term for the derogatory words themselves, but the process of using those terms within the group is variously known as co-opting, owning, or defusing in the examples I can find.
Not a single word, but consider contextually offensive.
Contextual:
Of, involving, or depending on a context. (TFD)
Context:
The circumstances in which an event occurs; a setting. (TFD)
Similar formulas might include situationally offensive or contextually derogatory. The challenge in finding a single word for this is, I expect, due to virtually all offensive words having this characteristic. There are very few, if any, that are offensive to every speaker of a given language.
The notion of “selective or discretionary enforcement” could be relevant to your question on two levels: as a base on which potential multi-word answers to it could be constructed (see several suggestions with caveat, below); and also as an example itself of a phrase that fits the phenomenon described in it.
Just as the dark past and present of derogatory words/epithets shows them being used offensively by people on the outside of a particular group against that group as a whole, perverse tools such as selective/discretionary enforcement (e.g., selectively enforced laws) have historically been similarly used by one group (generally the one in or with power) in an offensive manner against another group; both in attempts, historically and to the present day, to affix a badge of inferiority on the entire targeted group.
Likewise, when either derogatory words or selective/discretionary enforcement are used not against an entire other group, but rather among fellow individual members within one group, although their general negative connotations remain, the ‘targets’ of these two practices become individualized, rendering their purpose less offensive, at least on a bigoted, “us-versus-them” level (even to the point of being used affectionately between individuals, as you mention), than when used to attempt to injure an entire other group with single words or with selectively enforced laws and regulations.
If I have failed in my quick, off-topic attempt to equate (and partially rehabilitate) the notion of “selective/discretionary enforcement” with partially rehabilitated derogatory epithets in the context of your question, I still think you could consider using that notion (together with the notions of “self-enforcement/regulation/monitoring” as a part of the answer you seek, but please do so with caution because without rehabilitation, any use of “selective [self-]enforcement/regulation/monitoring” will probably imply a bias against such usage by those who, I firmly believe, are fully entitled to use such questionable words (as well as questionable tools, such a selective enforcement) that have historically been and continue to be used against them, however and whenever they need to within their own group, free from claims of “Hey man , no fair, if I can’t call them that then nobody can!” coming cluelessly from without.
With this caveat/warning in mind, here are a few suggestions, all phrases, as per your comment above in which you stated that you’re seeking “a word/phrase …” (and I’ve also included three suggestions at the top of the list that incorporate your good suggestion of “rehabilitate,” which would not, in my opinion, imply the negative bias mentioned above nearly as strongly as the remaining suggestions would, although the first two would lack, respectively, either the important notion of “self” or that of “selectivity”):
1) “Selectively rehabilitated words/epithets” (from “the selective rehabilitation of words/epithets);
2) “Self-rehabilitated words/epithets” (from “the self-rehabilitation of words/epithets, where the “self” refers not to the words/epithets, but to the owners/speakers of them, just as “Self-rehabilitated buildings” are defined in the US Tax Code [26, Section 47(d)(4), near the bottom of the linked page] not as buildings that have rehabilitated themselves, but rather buildings that have been rehabilitated by their owners);
3) “Selectively self-rehabilitated words/epithets” (from “the selective self-rehabilitation of words/epithets”);
4) “Selectively self-enforced language/word choices” (from “the selective self-enforcement of. …”);
5) “Selectively self-regulated language/word usage/epithet usage” (from “the selective self-regulation of …”); and finally
6) “Selectively self-monitored words/epithets” (from “the selective self-monitoring of …”).
("[S]elective enforcement occurs when government officials such as police officers, prosecutors, or regulators exercise enforcement discretion, which is the power to choose whether or how to punish a person who has violated the law." from Wikipedia)
("[Discretionary enforcement] refers to the enforcing [authorities'] power and ability to [make] their own decision or determination as to whether something will, or will not, be enforced." from Answers[dot]com)
(self-enforcing:adjective-1. "of or having the capability of enforcement within oneself or itself; self-regulating." from Dictionary[dot]com)
