Logically, since you asserted that he is a vegan, the onus is on you to back up your assertion. When you ask others to prove your assertion wrong, you are committing a logical fallacy by shifting the burden of proof.
Could you explain to the USMB forum, the reasoning that you used to come to the conclusion that he's a vegan?
When you claim that you are a vegan, it's relatively believable because the significant cognitive impairment that you consistently display in this forum is a common symptom of the brain damage caused by chronic vitamin B12 deficiency.
So far all you have provided to back up your assertion that he is a vegan is that he claimed to be a vegan. Do you automatically believe everything that anyone claims?