A sadist, a masochist, a zoophile, a necrophile, a pyromaniac and a serial killer are having a stroll in the park.
This merry band of weirdoes and deviants are getting a bit bored. Then the zoophile whispers: "Oooh, I know what we should do. Let's catch a cat!"

The sadist nods approvingly: "Yes! Let's catch a cat... and let's torture it!"

The serial killer licks the blade of his knife, and chimes in: "Let's catch a cat, let's torture it, and then let's kill it!"

The necrophile adjusts the front of his pants and grins: "Let's catch a cat, let's torture it, let's kill it, and then let's have some fun with its corpse!"

Toying with his lighter, the pyromaniac replies: "Let's catch a cat, let's torture it, let's kill it, let's have some fun with its corpse, and then let's burn it!"

The masochist is quiet for a moment.
Then he says:
"Meow."

I picked up a hitchhiker last night. He seemed surprised that I'd pick up a stranger. He asked, "Thanks, but why would you pick me up? How would you know I'm not a serial killer?"

I told him the chances of two serial killers in the same car would be astronomical.