As part of Gen-X, I feel like that's appropriating from my culture. I was proudly on the "slackers" mailing list as an adult in the 90s when the millennials were being born. Give millennials a new pejorative, don't steal ours.
Maybe the word "Boomer" will just get redefined to mean "old people with more money than me". Kind of the same way "meme" got redefined from "idea permeating society" to "cartoon or cat picture with sarcastic text", and how "troll" got redefined from "someone who tries to antagonize" to "someone who says things I don't agree with".