I'm not a nazi but it does get my goat a lot of the time, I often bite my tongue. Particularly your/you're, there/their/they're, less/fewer. Also the good, old apostrophe.
I left school with very few educational qualifications, but over time my spelling and grammar has improved immensely. If I can do it then so can you, one word at a time. Please.
Another bugbear of mine is pronunciation by my stepkids. Found has become fount, anything is now anythink. At least my daughter corrects her elders when they say glottal stops (t), and I hope she continues when she starts school in September.