Along with "epic", "just saying" is one of those annoying, overused terms that drive you crazy until they disappear. Finding this discussion has been an "epic" moment for me!
The Seinfeld origin appears to be the best answer. The reason I came here was because I have spotted the phrase in writing, on the internet, far too many times in the last week. It is extremely annoying because the author is not saying anything. They are writing it!