rant/advice needed

[ugly_fruit]

my boyfriend and i are both vegan. we just talked, and he told went to several grocery stores and couldn't find any seitan or tofurky for christmas dinner, so he might just eat the salmon his family is having instead. my intial reaction to that was obviously "are you fucking serious? just eat the vegetables side dishes and make pasta or something. it's not like you're going to starve." he got very defensive, said he feels "weird" making another food while his family already cooked a christmas dinner, and that the salmon "was already purchased anyway." though infrequently, this kind of thing tends to happen, such as the time when our roommate ordered a cheese pizza and didn't want to carry the leftovers home, so my boyfriend ate them. i'm glad he tries not to be wasteful, but still find his behavior aggravating. vegans don't eat salmon, end of story. this isn't even a situation of waste, it's a situation of convenience, & i'm not buying it. am i overreacting? is there a way i could talk to him about it that won't make him all defensive? i'm especially sensitive because he's the only vegan i know in real life, and i feel he doesn't take it seriously. just to note, i'm not a vegan elitist by any means, but...salmon? come on!

edit: he just let me know that he won't be eating the salmon, and apologized for making me upset (this is why he's the best boyfriend, haha). but still...for future reference. what non-attacking things could i say in a situation like this if it happens again? compelling arguements, etc. i'm going for effectiveness here. thank you guys :)