I asked this question not long ago, I now believe that everybody knows when they’ve had too much, there is warning signs in my experience but the defining answer is this: it probably becomes a sin when you can’t tell the difference between right and wrong, when you lose control.
In the past I used to enjoy losing control, getting drunk and forgetting about everything. You become somebody else. Which is something people enjoy.
However I think everyone is different and also the more you drink, the less the alcohol effects you, it still effects you but you can probably handle more than a person who drinks less.