So I'm walking the dog in the back yard and I encounter a Speckled King Snake. I've met quite a few of these snakes and once kept one as a pet. This little ripper coils up like a rattlesnake and begins shaking its tail furiously. I don't know if this guy has been hanging with a tough crowd, but I've never seen a SKS act this way. Is this unusual, or have I just never found an angry one?
So I'm walking the dog in the back yard and I encounter a Speckled King Snake. I've met quite a ... I've never seen a SKS act this way. Is this unusual, or have I just never found an angry one?

Tail rattling is a common defensive behaviour for many many species of snake. Some species (e.g., hognose) are well known for it, others not so.
When this group was very active, a great many people reported seeing tail rattling in a wide variety of snakes, I have the impression that some more excitable individuals in a species tend to do it, I expect that's who you encountered.
nj"has a very laid back hoggie"m

Welcome, stranger, to the humble neighbourhoods.