You brought Mace to the club with you and ordered some drinks. But, five drinks layer you needed to use the bathroom. So you left your drink with hum to guard. Due to the line that was growing, it was going to be a while before you got to see your drink again.

Mace kept the drink guarded, by drinking it. He couldn't tell the difference between his drink and yours due to the lights, but he accidentally drank yours, so the taste told him.

When you finally got out and went to Mace. He gave you his drink. "Here," he says. You could tell this wasn't your drink, he was just giving you his as a replacement.