question: what do you do with the glass you did not finish

the board is new so i will start small. not a ranking. a question.
when you pour a glass and do not finish it, what happens to the rest. i have a rule (cold glass, back in the fridge within the hour, i do not let it sit on the counter) but i have heard from a few people that they just pour it out, and i have never once poured one out, so i do not know what that feels like from the other side.
is there a right answer. or is it a glass by glass situation.
also if you have had a bad glass recently, i want to hear about it. not to argue with it. i want to know what went wrong so i can think about it. that is how you get better at milk.
i will read every reply. i will not rank any of them.