Once upon a time in Facebook land, when you went back to your friend's rant post, you could see if they had tidied it up or not by looking for "edited" beside the post date. Facebook took that gift away from us.
Now you have to do a little more leg work to prove that well-thought out post used to be a crazy drunken rant and you're not going crazy. Thankfully, you don't have to go total Sherlock. There's just a few more steps.
Go to the arrow icon in the upper right-hand corner and click it.
Click on View edit history. This works the same way for the desktop version and the app version of Facebook.
A nice list of all the versions of the post will pop up for you to look at -- or screenshot -- or whatever.