I can only speak for myself, but not eating meat is not something that’s offensive. Nothing about veganism as a diet is offensive or in need of being critical of.
It’s the reputation of them being insufferable and obnoxious. It’s their need to inject their diet into discussions that aren’t about them, or their diets. It’s the way they lord over everyone with a ‘holier than thou’ attitude.
And I have experienced all these things first hand- MANY times.
In short, the problem with vegans is that there aren’t enough positive and down-to-earth vegans to counter the bad ones.