Let your guests take their time and enjoy their drinks. If a guest does over consume, have another guest drive the person to their destination or plan on an extra house guest for the night. Don't let the intoxicated person drive even if it means taking the person's car keys away. If the person is convicted of DUI, the driver faces time in jail and suspension of his or her driver's license. It doesn't take a keen eye or great knowledge to know when a person is intoxicated.
Common sense goes a long way in detecting someone who is drunk.
If a person has difficulty in performing basic motor skills or has trouble remembering specific incidents or talking, it's a safe bet that the person has had too much to drink. The drinking of alcoholic beverages affects people in different ways. The amount you may be able to drink without adverse effects could be different than that of your friends. Even your own tolerance to such beverages will vary from day to day. Drinking drivers also have a tendency to drive over the posted speed limit.