Final answer:
A bartender should act responsibly when a customer shows signs of intoxication, potentially refusing further service and ensuring the patron's safety. Intoxication depends on individual factors and metabolism rate, with responsible drinking guidelines advising moderation.
Step-by-step explanation:
In the scenario where a regular customer at a bar is showing signs of intoxication after having only one drink, a bartender should take responsible action based on training and policy for handling such situations. This can include refusing to serve more alcohol and ensuring the patron's safety.
Regardless of the number of drinks consumed, if a customer shows clear signs of intoxication, this can be due to various factors such as a low tolerance, interactions with medication, or possible consumption before arriving at the establishment.
It's important that alcohol intoxication can be influenced by various factors, including age, sex, pre-existing health conditions, and the rate at which a person's body metabolizes alcohol, which is around 3.3 mmol/L (15 mg/dL) per hour.