ETA , as used to add something to your post after sending it.
E means “edit” , I assume. What,s the TA mean?
(And where is the smilie for "facepalm, I’m embarrassed about my post). 
Edited To Add
Estimated Time of Arrival. 
Eric the Actor
Look, I took the hit and gave the serious answer to tee you guys up. Let’s see some better efforts please.
Egad, thy anguish!
Extraneous Text Abridgment
Exit To Albuquerque
Eternal Trump Admirer
Embrace The Autogolpe
Existential Threat Anxiety
Enlightenment Through Autoflagellation
Emergency Tactical Abequitation
Everyone Thinks you are an…
Ok. edited to add.
Extra Tits n’ Asses.
η
Or H. One of those.
And with that, the occasionally used (at least outside of Mafia threads) NETA is Not Edited To Add. A separate post that you would have otherwise edited in to your previous post but didn’t or couldn’t. I usually use it to imply that I missed the edit window.
rimshot
Expensive Toolbox Addition.
My fave.
Extra Terrestrials Above.
It went away when the site was redesigned, but I saved it.
Enjoy This Addendum or Embrace Total Annihilation
It depends on the context.
Discourse has 2: male 
& female 
. They’re in the section labeled “People and Body” not “Smileys and Emotion”. Like most (all?) Discourse faces you can also adjust the skin tone.
I don’t much care for them; I think they look more like “peek-a-boo” than “Oh Shit!”
If you prefer a more belligerent interpretation:
Eat This, Asshole!
That’s one hell of a significant comma.
Enter The Aardvark