[PhantomGremlin]

casual old-fashioned ethnic slur

It's not a slur. Why does everything need to be so PC these days? The term may have originated in NYC, home of much colorful language.

Here's a Village Voice article that provides a lot of background and that quotes illegal cab drivers referring to themselves that way:

   once a gypsy, always a gypsy

http://www.villagevoice.com/news/how-some-illegal-taxi-drive...

[mfoy_]

>referring to themselves that way

Apply this logic to any other ethnic slur and see how well it works out for you.

[PhantomGremlin]

First, the drivers aren't even Romani. Second, the NY Times has used the phrase, quite often. Granted, with a quick Google I couldn't find a more recent NYT reference than 2008, so maybe they changed their mind.

Pulitzer Prize winning columnist William Safire, perhaps best known as a long-time syndicated political columnist for the New York Times and the author of "On Language" in the New York Times Magazine, a column on popular etymology, new or unusual usages, and other language-related topics[1], explains in the NY Times:

   Just because some people take offense
   at a word, however, does not automatically
   banish the word from the English language.
   ...
   it is hypersensitive to take it as a slur

http://www.nytimes.com/1986/02/23/magazine/on-language-gyppi...

Here the NY Times mentions that a politician was a former driver: http://www.nytimes.com/2006/12/16/nyregion/16rivera.html

[1] https://en.wikipedia.org/wiki/William_safire

[mfoy_]

>First, the drivers aren't even Romani.

This makes your argument worse, not better. The term "gypsy cab" derives from a racist stereotype of the Romani[1]. How can a term with a racist etymology not be racist?

Imagine any group of people appropriating traditionally-derogatory ethnic slurs for another group to describe themselves. How is that okay?

As for the Pullitzer Prize winner, that article is from 1986, more than a bit out-dated. Bizarrely, the author even defends the verb "to gyp" as not being racist because it's only one syllable. Imagine the sheer outrage if the verb "to nig" came into popular usage and referred to a negative stereotypical activity.

Why am I even arguing this? The fact that the term "gypsy cab" uses the name of an ethnic group to refer to a stereotypically negative trait of that group should completely and utterly speak for itself.

It's not "too PC".

[1] https://en.wiktionary.org/wiki/gypsy_cab

[PhantomGremlin]

Why am I even arguing this?

Because you don't agree with Safire, who stated quite clearly:

   Egyptians, from whose name the word gypsy
   erroneously originated, are usually unaware
   of the etymology and are not offended.
   (Gypsy cab, which uses both syllables,
   stresses the ''wandering'' meaning of gypsy,
   which is descriptive and not derogatory.)

Edit: You seem to be saying

   “When I use a word,’ Humpty Dumpty said in
   rather a scornful tone, ‘it means just what
   I choose it to mean — neither more nor less.’

Never mind the opinions of people who made a living writing about the meaning of words.