How could even a Nazi-like vegan not be satisfied with a bunless veggie burger, tofu fries and a diet coke to go?
Just no pleasin’ some folk.
In all seriousness, a statistically significant higher percentage of vegans / vegetarians are diagnosed with OCD. My dim recollection is twice as much as the rest of the American population. The prevailing theory in the mental health industry is that the rituals and hair-splitting of every aspect of eating, including food shopping and menu selection even in their own kitchens, disguises the disorder, which precludes treatment.
It is when they engage in what they think of as normal behaviors -- demands to inspect the kitchen, demands for use of "vegan-only" utensils, extensive querying of type and provenance of ingredients -- that the disorder can be seen for what it is, with the resulting conflicts with normal society.