I think much of my everyday speech would qualify. Particularly when I am tired, or nervous, I tend to speak with both more careful enunciation and, for whatever reason, an expanded diction; I become quite verbose. I ought to add that, while it's legitimately unintentional initially, I do play it up.
I have a pretty expansive vocabulary and I do enjoy using rather unconventional words whenever I can. Why use a monosyllabic when a sesquipedalian is available? Of course this is the tragic result of taking Latin and medieval studies courses at university. Recently I had to read an academic article where the author actually chose to use the phrase 'sedulous
Quellenforschung', and I have to admit that I had to look up the definition for
that! And now I am just dying for a chance to use that on someone.
No, but seriously I try not to be quite so pedantic a bore as that. I do, however, undoubtedly use many uncommon words. And I have actually taken a course that specifically looked at the Greek and Latin roots of modern English, in which I learned many fascinating words and their origins.
Some of the weirder ones that I tend to use in in normal speech are:
Irrespective: meaning without respect to, or regardless. The latter being what any normal person would use.
Extemporaneous: meaning something out of the moment, without planning, and usually used of speech.
Stentorian: meaning exceptionally loud, and coming from the name of Stentor, the herald off the Greek army during the Trojan war.
Post Script: and obviously this post is an example of a number of words which are not so common, but which sadly I am given to using in everyday speech. And I am being intentionally loquacious and pedantic as I pontificate on etymology.
PPS: Also I am proud to have been able to use several words which the Escapist doesn't recognize.
Edit:
Marter said:
One of my favorite words is "penultimate," which means second-to-last.
If there's an excuse to use it, I use it.
Here's a fun one for you based on that, and which you are unlikely to ever need to use:
antepenultimate, meaning third-to-last. Which I fear is actually a word. Also,
antepenult which is the third-to-last syllable in a word. Which is only ever likely to be relevant in the scansion of Latin, or maybe Greek, poetry.