A dumb, completely pointless holiday invented by greeting card companies to sell more cards. A concept that hasn't and (hopefully) never will catch on. On this day you're supposed to thank your boss for "being kind and fair" and buy him some stupid card, but really, its just a classic hallmark holiday. Ironically, most people seem to resent their bosses anyway so whats the point?
Joe: I got a card for my boss, because today is Boss's Day!
Mike: What the hell is "Boss's Day"?
Joe: Its a day where we show our appreciation of our boss!
Mike: You're an idiot who blindly follows dumb trends, you know that?