My first post was
Funny/not-so-funny experiences with controlled substances
funny story and got a mod on my back on the same 1st post for having too big a sig Thanks Coldfire 
As one of those that was a victim of the Great SDMB Crash of 2002, my first 30 or so posts vanished and will never be seen again. After re-registering, my first post was of course about the Great SDMB Crash of 2002.
What I thought was a rather witty response to Write your own Star Trek episode.
I almost killed the thread with my first post.
After lurking for a little while, I registered on 4 Aug. 2000 and made my first post in the thread Religious funeral practices.
I killed it. 
My first OP came three days later with Japanese Parliament = Diet. Why?, which did a little better.
(ok, preview keeps eating my posts, so please excuse any typos or coding errors)
My earliest apparently got wiped out in the Great Collapse.
My earliest post that is in the archives is a one-liner in a thread about Masons.
My earliest post is one wherein I posited that the return of Imperialism, in the form of a Pax Americana, would be a good thing, so what’s stopping it.
I am almost embarrased about some of my earlier posts.
My first post was to a thread titled “frostbitten doggie feet.” Being a sucker for anything doggie-related (since I have the world’s greatest dog), it inspired me to post for the first time. I’d registered on September 4, 2001. One week later, of course, the shit came down. And one week after that, I made my first post:
I think I killed the first 20 or so threads I posted to.
Oh, the thread is here. And I note that the OP apparently posted that one OP and then retired from the boards, as s/he still shows up as one post.
First post was my first thread.
Crabs with samuri on their backs?
Username yojimbo and I type samuri not samurai :smack:
My actual first post is gone. It was lost months ago when the server went down and the backup couldn’t bring it back. I had to make my name again and start from scratch. But I still don’t remember what I posted first.
I went through the rabbit hole a few weeks after I signed up, so this isn’t actually my first post, but the rest are gone, gone, gone. So this will have to do.
Does anyone know what Cecil’s first post to the boards was? I noticed that the “perfect master” has posted a few times, so I was curious if anyone had a link to it.
My first post, on November 2, 2001 was also the first thread I started… Naked Newbie Coming Out.
I received a warm welcome for which I am grateful.
This is my very first post!!! woohoo 
You know I actually was hoping someone would say that! Isn’t that a little…uh…uh…Okay, I don’t know the proper word for it…
EmmieMoon had her very first SDMB post in this thread too, on page 1. (Though she didn’t quite match Chicklet in excitement level. Woohoo!!)
I had the misfortune to register during The Winter of Our Missed Content ™ so my original posts AND user name (Frank the Lost Ramone) were wiped out.
My first post under my new, edgier, x-treem user name was about a song played in the theatre while waiting for the movie to start. It got not ONE…STINKIN’…REPLY!!! It wasn’t until this past summer I heard the song playing in my local bowling alley and I called 877-ROCK-300 to find out it’s called “Why Oh Why” by ATC.
No replies, yet here I am one year later going on 1000 posts!
Hi EmmieMoon ! Sorry that I missed your presence here on my first run through! Welcome to the boards!