I think veganism is an OCD paradise. I think it is a sort of eating disorder, because almost anything can be construed to be somehow indirectly related to cruelty to animals; it is just an excuse to try and have total control and obsess over one other (important) aspect of your life, without really needing much of a rational justification, since claiming to be a "vegan" pretty much lowers those raised eyebrows.
Out of curiosity, (iago), does your friend, or more importantly, anyone in his family (since his veganism almost certainly started through his family), seem particularly obsessive about things?