"Ever wondered where petrichor comes from?"
The man is staring a little too closely at you, like he's checking you out and investigating your face at the same time; neither of which you're very fond of.
You inch away from him, and yet you find it as some weird impulse deep inside to listen out his story, even though you're not really sure what he's talking about.
"Petrichor," he starts, his hands already in the air, "is the word for the pleasant smell after it rains. You know what I'm talkin' 'bout?"
You nod carefully.
"Yeah, yeah, so Petrichor. Where was I going with that...? Oh, yes. What petrichor came from."
You turn away. He's just going in circles by now.
"Wait, uh, petrichor...
person! Basically, it's from, like, this chemical the government puts in the rain-- like, y'know, the same stuff in the jet trails?
And it lingers after it rains, you see-- and that's why you always have to watch out for it."
He proudly stands up and takes a gas mask out of his bag, sliding it onto his face, and takes another one and offers it to you. "Stay strong against the government, friend," he says.
You laugh and take it from him hand. "I have an idea," you say, him grinning, "why don't we... y'know... go out back?"
You trace his shoulder blades. With a wide grin, you grasp his hand and drag him out to the alley out back. "Oh, uh, friend, I'm married--"
"Ignore that," you whisper. A glint of steel in the sun and suddenly, it's bloody, all bloody, and he collapses to the floor, body convulsing, ragged, sharp breaths through the gas mask.
"I'll tell you a fun fact," you mumble, dragging his body with most of your effort to the dumpster, "did you know that I take time to choose my next kill?"
His eyes go wide.
"Yeah, I pick someone mean, or abusive, simply assholish--"
Your eyes flick over to him.
"-- or someone incredibly stupid. Then the world improves instead of suffers when I choose to kill. It’s pretty simple, I’d say.”
You bury him in the trash and wipe off the blood with a paper towel, casting it into the dumpster with him. There's a light rain when you walk home, and a pleasant scent.
Petrichor, you've learned.