The act of which a user, in a format such as discord, posts something, then you, wanting to post something as well, do so, only for that person to post something similar (Slightly edited, or the same thing), basically throwing a fit because they're not getting attention
Jim:Ooh this drawing I spent HOURS on is done, I'm gonna post it!
KYLE:Ooh no! Someone posted after I posted MINE?! IM GONNA POST IT AGAIN
Jim:What the fuck dude, why are you sandwich posting me?
the feeling you get after you finish eating a darren turkey chip special
guy 1: Man, are you feeling alright?
guy 2: No man I just ate this sandwich, and now I think I've got post sandwich depression.
When the sandwich was so good you take the time to stare into the wind of how good it was
You ever had a sandwich so good you just had to reflect on its greatness = post sandwich reflection