The classic one is "should have" or "should've" to "should of" because when spoken, it really does sound similar. I don't know what the fuck people are learning in English classes these days though, or if they even still have them.

Not sure where you're from but in my dialect (North American) it's more common than not to have _have_ realized as [əv] ("uhv") in contexts like _should have_, _could have_ (but not _I have a car_, where it has to be the full [hæv]). Only in deliberately enunciated speech do I feel like I'd expect [hæv] in the former kind of context. So it's an understandable mistake to make.