The term "millennial" is used to describe people of a certain age who are apparently totally inept, live with their parents, have crippling student loan debt, don't know about anything pre-90s and totally vex and annoy older people.
This term gets used so often that most internet users think they have a solid idea of what a millennial is, so they throw the term out there as an insult whenever they don't agree with something a younger person says online.
But as you'll see in episode 63 of Ultra Spiritual Life with JP they have millennials pegged all wrong- because millennials literally don't exist offline.