The act of pouring one out — whether you do it for the Devil, your homies, or Dionysus — is an ancient tradition called “libation” that stretches back to early civilizations like ancient Egypt.
While “libation” is commonly used today as a funny way of saying you're drinking, it originally strictly referred to drinks that are poured out as an offering.
One of the earliest mentions of pouring one out comes from early Bronze Age Mesopotamia. Pouring liquids was a “vital part” of ancient Mesopotamian rituals.
According to Atlas Obscura, the ancient Romans installed tubes that drained into graves, allowing grieving loved ones to pour libations directly into their deceased family and friends’ burial spots.