This one enrages me. It's so specifically ignorant you have to do it on purpose.

The people that do this absolutely know that "should'f" isn't a word, and they don't flinch when reading the word "should've". How can they possibly think "of" makes any sense?

They're going out of their way to make English harder to teach and learn when they goof it that hard, and you just really have to be so stupid to do it in the first place.

I'm all for subtle language evolutions, but doing things wrong on purpose isn't the way. But if anybody calls them out they do the equivalent of "nerd!" and ignore the correction.