See if he admits that he is drunk. People who are really drunk are out of their minds and don't realize they are drunk at all. So people who say they are not drunk or don't want to talk at all are really drunk. On the contrary, people who say they are drunk are conscious. The reason why they say they are drunk is that they want to go crazy through alcohol.
Look at the action response
A really drunk person is paralyzed and confused. If you hit him, he has no power to fight back. If you hit him, or before you hit him, he will get down first. If you hit him, he will fight back, and his hand is still strong, which shows that the brain can still dominate the body and react. He's not completely drunk yet, he's just pretending.
Read the intention after drinking.
People who are really drunk will feel very uncomfortable, some vomit wildly, and then just want to sleep, no matter where they fall. People who pretend to be drunk will have some attempts, either to quarrel with others or to be close to girls, and they will have full stamina when they speak.
Look at the way you walk
Drunk people walk with exaggerated postures and shake badly, while really drunk people are weak, like beach mud, unable to lift and keep sinking, and their legs have no strength to support their bodies, let alone shake greatly.