I can drink a pint of liquor in about 3 hours and be totally fine?

I will occasionally drink on weeknights, not a regular thing, but when I do I get a pint of whiskey or vodka and finish it. I don’t get overly drunk and am able to wake up for work on ab 5 hours of sleep, go to meetings, and perform. But when I go out to the bar and drink the same amount I wouldn’t be near as functioning. Typing this after drinking a pint of Tito’s. Any explanation?