I get it. It's something I notice almost every day. The worst is when people say things like "I literally died and went to heaven". Arg. If you are an English teacher, by all means do your job and teach English as it is meant to be written. I wouldn't lose sleep over it though.
I like to think about how the English language has evolved over the centuries and realize that what we consider correct in 2014 has not always been considered correct. Imagine people from the 1800s reading this thread. I grew up in England and had to come to terms with US spelling which never made a whole lot of sense to me. Why change the spelling of words? Now I live in Canada, which seems to be stuck in the middle, slowly transitioning from English to American thanks to the internet.
We can follow the rules but there will always be those that are unaware of them or purposely ignore them. New words come in, new spellings, new meanings. I think what matters most is the clarity and quality of the message. I know what people mean when they say "I literally died and went to heaven" so why should I care? Besides, I can't even be bothered to use correct punctuation any more. Or should I say anymore?
As for the dad, I suspect that if you really liked him, you wouldn't care if he could spell.