A pretty stupid and/or egotistical person, which is not illegal. I have literally met people who think like that. Also that’s arguably the most dangerous part of drunk driving: impaired judgement makes you think you’ve got everything under control, and you’re not that drunk anyway, and you’re a good driver… Combine that with someone whose brain isn’t exactly firing up on all cylinders when they’re sober and you’ve got a deadly cocktail, and also probably someone who is more likely to get too drunk to legally drive (and not give up on driving home after that line is crossed)