Vegans are kind of like born-again christians about meat and animals I think. Instead of seeing the light and learning a higher truth about God and Jesus, it's about animal rights. With vegetarians I know people that are that way because they don't like meat or are strict buddhist or whatever, but with vegans it's always they have found a Higher Truth. Because of that I think they feel they have the moral high ground and get preachy.

Honestly though, the worst offenders are the vegetarians that have a cat or dog and stick the poor animal on a vegetarian diet that it's not really able to survive well on.