This was all with one flatmate...
I bought bison burgers (expensive...a pack of 8 was $20 CAD at the time) and then actually replaced it...with beef burgers that were $15 for a pack of 20. Not the same thing on a nutritional level (I had to watch my fat intake due to lingering issues after gallbladder removal and was dealing with B12 issues - bison is lower in fat and higher in iron and B12 than beef). His reasoning was that he had seen me eat burgers before, so that should be fine.
When I was making cookies for people at work like I did every year for the holidays, he came into the kitchen and was like, 'That looks good.' and went to grab one from the cooling rack. (They are good. People raved about these cookies.) I told him I'd hurt him if he touched them because it was for gifts for other people. I ended up getting a mini-fridge with a freezer for my room so I could have some food he wouldn't touch. Although one Thanksgiving I had people over and the food wouldn't fit in my mini, so I had to label everything saying that it was for my upcoming guests and if he touched it there would be trouble.
His girlfriends (that I never saw - they always came in and left when I was either asleep or out and I spent a lot of time in my room anyway) would use up all my pads. I went to grab one from a pack that I bought the month before and there were one or two left. They also would use my shampoo and steal my hair clips. (I know the hair clips are a small thing, but when you have a lot of hair and need the bigger ones to contain it all the cost of replacing them adds up over time.) I ended up changing to using a cup instead of pads so they couldn't just take things and kept all of my toiletries in my room. I also switched to the 'no shampoo' method of hair (which actually worked better for my hair) so they couldn't just take my shampoo and conditioner.
He also never bought TP or anything like that, I was the one always supplying that stuff, so that also ended up hidden in my room and he had to get his own. It would have been one thing if he had bought it too for the both of us to use, but he didn't so he was on his own for that.
The final straw came when he was out of town and the police came knocking at the door asking about his girlfriends and if any of them were younger. I had seen shoes of people I didn't know at the door, but I legit never saw them, so I couldn't say what they're ages were. I started looking for a new place that day.