Then there is the cramping. Replenishing electrolytes when you leak as much of them as I do is hard. There is a really good chance I will get a moderate to severe cramp if I drank the night before. I think you are underestimating how significant a drink can be to someone training hard. Especially someone older, such as myself. You have to make a very large number of assumptions to arrive at your conclusion that is obviously incorrect for many athletes hobbyist or otherwise. Some guys can pull it off, and there are a few in my gym who can drink hard, come in hungover and survive a hard training session. That isn’t me or most people I know (anecdotally).
Just a thought if you're noticing a single drink that much.
That substance is not exactly harmless.
Edit: Assuming the standard definition of drink that's roughly equivalent to one light beer or one shot