A vegetarian so extreme that their insistence that others give up meat verges on totalitarian propaganda.
Vegenazis are usually such arrogant douchebags, and come up with the most ridiculous reasons for their vegetarianism, that even other vegetarians want to eat a nice bloody steak after dealing with them.
Vegenazis typically refuse to acknowledge any downsides associated with vegetarianism, and refuse to acknowledge any upsides to eating meat, or will claim anything negative about vegetarianism and positive about meat eating is a conspiracy orchestrated by the meat industry.
A vegan who is almost Nazi-like in his or her belief in veganisn, such that they feel the need to feel enraged by anyone who eats any form of meat, and go on a vegetable-fueled rage about how "meat is murder" and that meat eaters are "disgraceful, uncivilised, barbaric and primal" beings that should have gone extinct around the time of the Neanderthals. They also don't accept that going vegan isn't the best thing that could happen to anyone, and refuses to listen to anyone who says otherwise.
"Dude did you see the shitstorm in the comments on Deadmau5's Instagram photo of a suckling pig?"
"Yeah, those veganazis are back at it again with their fascist views of vegetablesuperiority. "
A self-righteous vegan who pushes his or her views onto others and will use violence, lies, misinformation and other unethical methods to promote their views.