It wasnt so long ago I caught more flak than a Lancaster over Berlin for raising the issue of a (theoretical) drunken flight crew member on another thread.
Alcohol gets burned off in the system at a fairly constant rate of about 1 unit every 90 minutes. If I was in a bar and there was a person there who drank more than could reasonably be metabolised before flight and I saw him walking through the terminal wearing lots of scrambled egg on his hat then yes I would raise concerns. Loudly and vociferously.
If the person had a couple of beers and left it at that with a decent interval before they took charge of an aircraft... not a problem. Its not so much a legal requirement to report someone as just plain survival. I wouldnt get in a car with someone who had consumed more alcohol than the legal limit, let alone an aircraft.