Writing "should of" in a very informal setting such as on reddit, also it's rage bait which is a bonus.

if you're in a casual speaking situation and you're imagining the words "should of," it's actually fine because it sounds exactly like "should've." You can think of it as an idiom accent being portrayed.

In casual informal socialising "should of" even though grammatically incorrect can be used just like any other word in a similar manner as long as it is perfectly understood, accent writing or broken English is absolutely fine.

Anything other than casual informal media then "should of" technically means nothing but you can still use shoulda woulda coulda.