Is it normal to get annoyed when people are rude to others about their grammar?
Also, spelling and all that. Specifically on the internet. It's like people forget that people from other countries are online. Sometimes it's pretty obvious that the person typing does not know English completely well. It's probably their second language that they are working hard to learn or perfect. Then someone is rude to them about it? And the people being rude probably don't even know anything other than English, so it's not very fair for them to insult someone's second language when they don't even have one.
Obviously this isn't always the case, but there's no way to know right off, so maybe keep that in mind when you start to insult someone for being unintelligent.