Being vegan. Yay vegans, eat what you want, live ethically, you are not all insufferable sanctimonious pricks, etc etc.
Things that are not ok: Leaving your roommate an off-the-chain straight-up aggressive note telling them they’re no longer allowed to have any animal products in your shared space, and then implying that they could stand to lose some weight (although in the vegan lady’s defense, I totally understand her objections to SlimJims and Spam; I’m not sure she needed to call them “trashy snacks” where “gross” would have done just fine, but I see her point that mechanically-separated chicken is indeed quite gross).
I cannot wait until my roommate gets home and sees the note I left her, telling her that in order to respect my dietary preferences she is not allowed to bring any food item into the house that does not involve cheese, wine, shellfish or asparagus (I’m really feeling asparagus lately, BACK OFF).