Some thoughts on this story:
I used to have a running gag with an old roommate of mine, which was this: when someone on the phone asked one of us what we were doing, we would answer: "oh, just fuckin' the dog".
We had no dog. I'm not sure if that's why it was funny to us. "Fuckin' the dog" was the catch-all phrase meaning "I'm not really doing anything worth mentioning". I would like to reinstate this practice using the phrase "killing a vampire".
Also: I believe the culprit may have answered "killing a vampire" because he didn't want to say "I'm beating the peacock!".
Also: I once had a friend who went a little nutso. I recall a party at which he, in all earnestness, proclaimed that Grimace was a vampire. I wonder if he was the one who attacked the peacock.