Reaction memes in form of a social media post/comment aren't that rare and on the other hand regular memes in this form are extremely common. I don't see where the surprise is coming from. The threats are very common as well when it comes to reaction memes, just look at those 2 quick examples:

And there are countless other memes where gun or arson are in topic. Those are practically a specific shitposts that you can send to someone as a reaction to something.