I assume that most vegans are pleasant and intelligent people with great senses of humor. However, I do not have any direct evidence to support this assumption.
I just assume that, just as Dawkins and Harris and Myers and (from beyond the grave) Hitch are making us (atheists) all look bad, so the humorless, self-righteous and just generally stupid among the vegans, because they make so damn much noise, are making vegans in general look bad. Surely you've heard something along the lines of: "I'm a vegan, and the joke you just told offends me because[...]" and the remark ends with something other than "[...]because I'm a humorless stiff."
There are few atheists who are constantly jumping up and down and yelling, "Hey! HEY! I'm an atheist, and I hate the way that the New Atheist keep talking about historical topics without bothering to learn about them first, and I've actually read the Koran, and I don't think we all should be afraid of Islam. Muslims are pretty much just people like others," and so on and so forth. In fact, I may be the only one.
Likewise, there are few vegans jumping up and down and yelling, "Hey! HEY! I'm a vegan, and I have a sense of humor! You could even tell me a joke about vegans and I'll probably think it's funny. Especially if it's a joke about those vegans everybody hates because they have no sense of humor! 'Everybody' meaning 'including almost all vegans', cause Duh!"
I assume that almost all vegans are like that, even in the absence of the jumping up and down and yelling.
The alternative would be to assume that a sense of humor actually is dependent upon ingesting animal protein and fat.