The Catechism is not intended to be a moral theology textbook or course.
When it is excessive it is sinful. When drinking is contrary to temperance or health etc.
Examples of when drinking is grave sin would be - total loss of ones reason, or it leads to other mortal sins, and of course drunk driving as you noted.
I do not know what a “few” drinks is for a particular person… (and body mass gets involved too)…but yes such can become sinful and could potentially be mortally sinful (such as getting drunk where one looses ones reason…).