If the bartender says to someone “you’re cut off” it means they can see you have had too much to drink and they will not serve you any more alcohol.
Sometimes someone will tell a bartender, you need to “cut someone off” someone else notices the person has had too much to drink.
At Club Blu, there were 2 bartenders working. Roxanne had been drinking all night. She was starting to get loud and have slurred speech. One bartender said to the other, if she comes to order another drink, tell her, “Sorry, but you’re cut off.”
Rob and Barry were out at a sports bar. Throughout the evening, Rob had two beers. Barry had 4. Barry waved over the bartender to order another beer. Rob shook his head at the bartender, to signal him to cut Barry off.