I’m sure some people use various words that other people never use. That is part of what “pretentious” means. “Pretentious” itself is a pretentious word. I could just as easily say “fancy”, “showy” or “extravagant” (though the last is “fancy” as well).
Then why did you say:
I use it IRL. I guess it’s not pretentious for me to use it here then!
It was a figure of speech, a '“trope”.
But “meme” is none of those. While I can’t say I use it much in spoken conversation, I see it frequently in print media including general circulation newspapers and magazines. It has a meaning that is distinct from other available words, and I think it is commonly understood.
Just because a word originated after 1975 and you don’t use it yourself doesn’t make it pretentious or fancy.
That’s a fancy meme you got there.
The neverending hijacks and nonstop bickering over trivia 
As I said, I don’t really care. I’ve already spent more time on this than it is worth, and didn’t even bring it up in the first place so obviously I’m not alone in the opinion.
That’s a feature, not a bug! 
Some would call it a cliche.
A pretentious pedant would point out it’s cliché (with an accent). 
“Meme”?