Say there’s a young lady* who has a single mixed drink or a beer every night or so, because it tastes good. She nearly always drinks with food or nurses the drink for an hour or so. She never gets drunk and rarely buzzed. Would said person’s alcohol tolerance increase?
(Just curious, and yes it’s a pointless question)
What do you mean by tolerance?
I ask because the usual definition that I’ve heard has to do with needing more of a substance to achieve the same effect. So if the effect you feel after having that drink (or skipping a night) hasn’t changed over time, then I’m not sure what a meaningful measure of tolerance would be.
I think she means if having 1 drink makes you tipsy, if you do it night after night at some point will having 1 drink no longer make you tipsy?
Yes, that.
Last night, aforementioned young lady had a drink that skipped tipsy straight to ‘I’m going to bed now’ (Blue Mountain Bronx, in case you’re wondering. With two shots of 40% alcohol rum. [well, there’s your problem right there]). If she continues to drink her usual drinks, the ones that at usually don’t make her buzzed (they generally have one shot of 40% alcohol vodka, or ~20% alcohol soju), could she drink more without getting buzzed?
Because the drink last night tasted really good, but damn, the side effects were not that fun. … Or so I heard. 
IANABiochemist, but my understanding is that hepatic alcohol hydrogenase is an inducible enzyme. So, tolerance over time should increase as the liver gets “better” at breaking down alcohol.