A Short-Sleeved Genius is a person, usually a male, who abuses their minor managerial role within a business setting. This person utilizes their limited power to assert complete authority or assumed knowledge in an aggressive manner. Think a psycho Pep Boys manager or Dwight from The Office. While anyone wearing short sleeves and a tie is a potential Short-Sleeved Genius, it is not a mandatory dress code.
I was at the DMV getting my license renewed when some Short-Sleeved Genius told me I was in the wrong line. He threatened to "write me up" if I didn't change lines. WTF, I don't even work there!