A good product evangelist is someone who can talk about the people they've met in the same way regardless of whether or not those people are still in the room. That is the skill that makes you good at evangelising something - if people like you they'll listen to you. If people see you being nasty they won't, because they'll wonder if you're going to be nasty about them once they leave.
If we're gonna hold words against people, well obama isn't president material, because you remember that one time he said the N-word. No president should use racial slurs. You see what I'm getting at.