“Being an alcoholic” is one thing, and I know more than a handful of people who have been high-functioning alcoholics through my life and various career paths so far.
However, that I know of, I’ve only noticed one person who showed up to work drunk, and I had to dismiss him (from work) the night that I discovered it, so that he could be fired the next day when the payroll and timekeeping folks were on hand to give him his check.
I’ve had my doubts about some people’s performance based on speech patterns and occasional missteps or stumbles while walking, but … in the construction trades one finds poor speakers all the time, and stumbling over sometimes rough ground is part of the job. So those are poor indicators as a general rule.
I once attempted, back in the days when liquor at office Christmas parties was a regular thing, to offer a neighbor / co-worker a ride home because he was clearly drunk, and he sobered up just enough to threaten to punch me if I suggested it again. I would handle that differently these days, but back then I simply waved it off and let him do what he was going to do anyway. He lived; most drunk drivers generally do, after all. And he didn’t have any mishap that I ever knew about.
In fact, several years ago we had a different sort of office Christmas party, at a nice restaurant with a great dinner. But I had too much wine with the meal after a couple of mixed drinks before dinner, and I felt myself to be incapable of driving well enough to trust myself, even though “home” was less then ten minutes away on roads that I knew well. So after the luncheon I went to my car – in a parking garage – reclined the seat and played music for a couple of hours while I dozed. I guess I really could have been cited for “operating a motor vehicle” while under the influence, which would have been technically true, but it still seemed like a low-risk move.
So … context matters. I don’t currently know or even suspect any of my associates to be alcoholic or drug users, but if someone had an acute problem at some point, I’d still attempt to help them through the current crisis, and depending on their reaction I would act differently than I did in the early 1980s. I’d cut his tires’ valve stems, or call a truck to have his car towed, or get other friends to assist in taking his keys, if we couldn’t get him drunk enough to pass out, for example.~
But as to those who “drink a lot in the evening” but show up to work, and seem to work well, afterward, I’d still leave that alone.