It's more likely than you think.
One day John finds himself surrounded by vampires, but they're just going about their business like any human would during the day. Is it wrong to kill them? John doesn't think so as these vicious things kill people at night.
There was one in front of him, one behind him. Waiting in the Post Office queue was a chore already, but being around these vile creatures made John's blood boil.
The other people just let the vampires live their life and just stayed away from them, but they didn't know what John knew. They kill.
He wanted to stick a knife between both their eyes.
Fucking bloodsuckers. Do not want.
"Hey John, come to collect your wages?" said the Post Office clerk.
"Yeah." John said bluntly
The clerk hands an envelope to John.
This is relevent to my interests.
John makes his way out of the Post Office, seeing yet more of the vampiric demons.
On his street he sees one, just one, solitary, alone. The perfect opportunity. John pulls out a knife and sticks it into the back of the vampires skull.
It could've killed my family in an horrendous way.
John went into his house, feeling a little better.
"Humans have begun killing us" said the head vampire, Vladmir Chan, "we must retaliate."
An army of vampires readied themselves for war in Castle Stoker. Their war begins tonight.