Some users seem to consider the name of the bot offensive, and have presented a lot of alternatives.
some of those suggestion was grammarnazi_bot?? because the first time you get visited there is no way to know at first glance if it is a bot or not, and maybe if you know that is a bot may help to reduce the negativity towards it.
Another suggestion I have, in relation with the previous one, is to change the message to start with:
Hello, I'm the Grammar Nazi Bot, I have found that you have....
That way you know that is a bot and not some, as somebody put it, a purist asshole or something that have nothing better to do...