Not eating meat, not eating dairy.
The harm to oneself is just nonsense. Most of the fittest and healthiest people are not vegans, they just have self control. It's a common trait of vegans to compare groups with preselection bias (those who already care about their health but are misguided in their methods) with all others, including all the fat clams who spend their days eating Iceland food and Greg's.
The harm to animals issue is just personal preference. Cows are tasty, so I eat cows - there's no need for it to be any more complex than that. For someone who claims to care about animals, you clearly haven't thought through what would happen to the cow population if we were all vegans. You're essentially cow Hitler, promoting methods that would destroy their population.