Which kinda is the point of this meme. The usage of 'Normie' has gotten mainstream and everybody refers to each other as 'Normie' implying that they themselves differ. But you know, most people differ a bit. Mainstream is mainstream, but just because you are using a "special" website, that doesn't make you abnormal.

I'm confident normie comes from 4chan, I've seen it thrown around there since long before it became mainstream, but there they were using it to refer to people living normal lives, something they (mostly) wanted to achieve. (I.E.: "I've got a girlfriend, I'm finally on my way to become a normie")

Now in its current usage it is more like an insult, something like saying "you are a basic bitch", which implies that person who said that isnt.