Ever since The Master mentioned it in an old answer, I try to use “albeit” in casual conversation as much as possible.
Albondigas. I don’t get to use it very often, but occasionally the cafeteria here at work has it on the menu, and I come back and announce to my neighbors, “Albondigas!”. Another favorite is baggywrinkles; every time I see a sailboat with them I have to point them out just so I can say baggywrinkles.
I also used the word “martinet” in a conversation today. I don’t think that guy knew what the heck I meant. Last week I had a similar reaction to “bifurcated”, which kind of bummed me out.
Here’s a fun one: Akimbo.
mmm
Floccinaucinihilipilification.
Boustrophedon - Mowing a field in opposite directions on each adjacent pass, or, writing alternating lines of text backwards.
and, from the German, *abfahrt *(exit)
most people seem to prefer Ausfahrt. 
:DMy son thought it was so funny he took a picture of an Ausfahrt sign when he visited Germany.
Crapulous!
I am fond of “octoroon.”
Umbrage, though I always want to preface it with “I say old bean” which is rather inconvenient for the expressing of offence. I suppose I could say “I say old bean, I take umbrage and you’re leaking didactic effluvium in my direction in disheartening measure” but that doesn’t help in gang violence situations as much as one might think.
My favorite usage of that term. (Video has two swear words)
My favorite is skeuomorph. Very useful word.
Which reminds me of a fun new word of recent origin - “octomom”
Which leads me straight to my fav new word - “refudiate”. Ah, Sarah Palin, you little semi-literate Shakespearean vixen you!
Syzygy. I’m always on the alert for a spot to use it. I think it drives my interest in astronomy.
This word is unknown to OneLook Dictionary Search and, apparently, even to Google (except as the name of an Australian horse*). Would you care to explain?
*My sister used to be in charge of naming all racehorses in Australia. I wonder if she was responsible for this one.
Well since callipygian has been taken a few times, spathic.
Mendacity/mendacious/mendaciousness. Basically it means “bullshit”, and “he’s BS’ing” and “that’s all BS”, but it’s more fun! (and educational!)
Serendipity: a happy, accidental discovery; has connotations of being kind of pre-ordained. I actually really like connotation/denotation, too. But while I’m pretty sure most Dopers are familiar with these things, most ‘normal’ people aren’t. 
My 20YO daughter who is going to Rule The World one day (really! She means it!) says that when she does, she’s going to make me her “Minister of Good Words”. 
I use that regularly.
I rather like to find ways to sneak concatenation into the conversation.
Photosynthesis
Boustrophedon has always been a favorite.
I also like ‘Usufruct’ - it sounds vaguely dirty. I put the blame on my copy of Black’s.
Hehehe… made ya say usufruct.
Damn…that’s the one I came in to say.
A text conversation with girl I’m interested in from yesterday:
She: “…but then you might think I was weird or something.”
Me: “You need to stop using using ‘weird’ as a pejorative.”
She: “Sorry, you’re right - I’ll stop that. Good word usage, by the way.”
Yep…her stock instantly jumped a few points in my book.