I hate when people say must of instead of must have
Don't you think you're exaggerating a little bit? Why are you bothered too much when people say must instead of must have?
I think people who make the mistake because they don't know any better should apologize instead of me
It is okay to have a pet peeve with grammar. People should be expected to know the grammar of their own language, but you shouldn't bee too bothered by it and be unreasonably be angry with someone if they said something that is not grammatically correct.
I what to know why people with low intelligence use it as an excuse to copy other words.
I think I have understood your point, but it feels like it's more than a pet peeve and you are actually thinking that you are feeling superior against people who do not know how to use grammar properly. If you have met someone who you need to correct their grammar, try to be respectful and try to tell them you're there to help and not be insulting.