I don't think "anachronism" is highfalutin because I don't know any SIMPLER way to say it. The Internet Movie Database, imdb.com, is essentially a popular culture site, not a cineaste's site. For every movie, imdb.com has a list of "goofs." Not "errata" (highfalutin), not "mistakes" (plain English), but "goofs" (colloquial). They are not trying to be pretentious or highfalutin. Movies set in historical times will usually have errors like the one spotted in "Robin Hood, Prince of Thieves:" "Azeem is shown using a refracting telescope, which was not invented until the 17th century." imdb.com calls this kind of goof an "anachronisms." What else COULD you call them? m-w.com shows me many rhymes, but no synonyms. Their definition is "a person or a thing that is chronologically out of place." That's four times as long as "anachronism," and uses a 15-letter Greek-derived word to define an 11-letter Greek-derived word. "Anachronism" isn't a simple word, but what else could imdb say would do the job? "History goof?" "Century fail?" "Scrambled time?" "Persons or things that are chronologically out of place?"

It depends who you are talking to. I'd use both of these words with my friends, family and colleagues. The use of these words assumes a certain level of education and knowledge on the part of the listener, but they are not pretentious in any way.

In the United States, it would depend on to whom you are talking. I am "college-educated" (i.e. university) and have college-educated friends, and among them I might use that word or expect to hear it used. I don't go in for that kind of role-playing but there is a "Society for Creative Anachronism" that likes to play at being 17th-century Europeans. imdb.com, the movie site, which is not a "highfalutin'" site, has lists of goofs in movies, and they call anachronisms "anachronisms." "Pro bono" is not something that would normally come up in conversation, but if a lawyer were doing charity work the language I would use is "doing it on a pro bono basis." On the other hand, I am occasionally a substitute teacher in the local high school (secondary) and I would not use these words talking to 15-year-old students. Colbert is joking. He is satirizing the anti-intellectualism shown by some people on the political right.

I cannot say what others use but i do not know anyone who would not think these are highfaluting words! These would be for my general conversation in 99% of places! Especially anachronistic! People would look at me funny. Pro Bono many would understand but wouldn't use in most circumstances unless speaking withe solicitors or academics. Most people would say 'free work', or i worked for free, my solicitor did that work for me for free, and this would be widely used and understood by anyone. As for anachronistic well only in academic perhaps or business circles or people wanting to impress others, I have never heard anyone say it! So maybe we are less formal than you think here!

It's possible that Colbert was joking and making a veiled reference to his audience, but in general I would say both of these words are quite common in context. Certainly in the US, pro bono legal work is commonly known and talked about, and is talked about in TV shows with enough frequency that anyone might be expected to know it. In the UK, there is also a fine tradition of solicitors doing pro bono work. Where it might not be so readily recognised would be other parts of the English speaking world where pro bono work could be known by other terms. For example, in New Zealand and Australia I have seen pro bono work described as community assistance. Anachronistic does tend to be a word that people without a higher level of education wouldn't know, but amongst graduates and professionals I'd anticipate it to be fairly widely used, though perhaps not frequently.