ParanoidObsessive posted...
I would, because just on the most basic level you're dealing with hygiene and freshness problems - constantly taking milk out then putting it back will cause it to go bad much faster (and you're absolutely backwashing into it each time, which leads to bacterial growth).
If you keep a separate, empty container that you put the cereal milk into and you draw from that first each time, topping up each bowl with fresh milk as needed, you'd mostly be okay provided you washed the container regularly and made sure to fully use it up every week or so (maybe by baking something with Friday's leftovers or something). It's 100% not best practice and any actual food service establishment doing something like this would get nuked by the health department the instant it came to light, but provided you're sensible about it you could do it safely on a personal scale.
ParanoidObsessive posted...
And I feel like it implies deeper mental health issues.
It definitely does get into hoarding/phobic levels of avoiding food waste (speaking as somebody who is more than a little neurotic about food waste). Milk may not be cheap, but reusing that quarter cup per bowl instead of drinking it on the spot or just throwing it out is barely going to save more money than you're going to spend heating and running the water needed to clean the container as often as is necessary.