I drink out of my milk container and my roommate knows it. He told me the second week I moved in that I am welcome to anything he has in the house, but warned me he drinks out of his juice bottles. I warned him I do the same with my milk. Yet, he still borrows my milk from time to time. I don't know if he forgets or what, but I'm never around when he does it (I just realize the next time I go to get it that the volume is lower than the last time I put it away) and I'm NOT going to stop drinking out of MY milk jug just because he borrows it after I already told him I do it. I think I'll put a post-it note on it next week telling him I drank out of it. It's not that I mind sharing, especially since he shares as well. BUT it's something that I've always done and I don't think I should have to change it.