A friend of mine once overheard someone in a bar order a drink by the name of Biohazard. It was a mixed drink, light blue in colour, served in a tall glass.

Upon serving, the bartender cracked an egg into the glass. As the egg yolk sank to the bottom of the glass, the drink turned clear, while the yolk turned green. The patron then drank it. My friend finished his drink and left. Quickly.

If someone with a well-stocked liquor cabinet and a yen for experimentation could figure this one out, please share. Blue curaçao seems a likely starting point.