1) Pertaining to hipster subculture. Derived from previous uses of "collar" to describe class: blue-collar, white-collar, green-collar. Conotes the, perhaps, more mature subsection thereof.
2) Used to describe a class of
professionals (after the fashion of white-collar, and blue-collar) who work in fields associated with
information, creativity, social-media, etc.
3)
Liberal arts majors who manage to get a job where they only wear ties if they feel like it, and with the top button undone.
Hipster 1, "Winston just got a job at the Huffpo as a social-media
coordinator."
Hipster 2, "Totally, kewl, joining that plaid-collar workforce."
"Dude,
I forgot my rooibos tea, at the new lunch-time yoga studio...man, I'm totally a
plaid-collar worker."