When it causes an inability to serve others and oneself according to the will of God.
Interesting concept, since in the "first miracle" - at the wedding feast - it was apparently okay for the guests to really party down - and yet, in other situations
.driving, at work, etc, the bar would be far lower.
From a legal standpoint, it begins when you take the first sip of an alcoholic beverage. Its unacceptability on the highway, for most states, is when imbibing brings the BAC to 0.08%; for most the equivalent of one bottle of beer, glass of wine, or shot of distilled liquor.
When it causes an inability to serve others and oneself according to the will of God.
That means at any point, when one is setting an example. Avoid the appearance of evil = God's will.
IMHO
(from one once classified 23 years as a habitual heavy drinker, now abstinent for 28 years)