Leaving the milk out

We have had a recurring problem with the milk not being placed back into the fridge after it has been used.. It's come down to me placing a post-it note on the milk carton with the remark "I require refrigeration. Put me back in the fridge!", which worked for a few days, but now has no effect. I decided to confront my flatmate about it. "Could you please make sure you put the milk back in the fridge after you use it?" says I. "Yeah ok... but UHT doesn't require refrigeration so it doesn't really matter". I almost exploded into a fit of rage, but doing so wasn't going to help the situation. "First off, this isn't UHT milk. Secondly, UHT milk can remain un-refrigerated until it is opened. This milk is open. This milk is not UHT. Refrigerate it." "Oh, I thought it was UHT".
Today's reason my flatmate pisses me of is that she continuously leaves the milk out, and has absolutely know idea about the whole concept of Ultra high temperature treated milk.

