Blink-And-You’ll-Miss-It Etiquette Lesson #3
If someone you know says "hello" to you as they pass you--in the hall, the breakroom, wherever--it is not acceptable to smugly raise your eyebrows in response. This is behavior most commonly perpetrated by but not limited to men. It's meaning is unclear but implies a certain supercilious disinclination to utter a simple word. It also implies something vaguely hostile.