Harry crossed his arms and tried a different tack, "You are so unbelievably petty." He was glad that he managed to make that sound ... strong and insulting, rather than whining and upset.
"I'm nearly never petty without a good point." Snape countered.
Well now, that was an idea. "You know that someone's coming to Hogwarts - but you don't think I could guess, or you'd have told me." Harry said slowly, "But... I am certain to do some form of wrongdoing in the next twenty-four hours - not to the level of being expelled, but merely getting detention."
Snape nodded slowly, his eyes sharp.
"Is Victor Krum coming to Hogwarts?" Harry asked, getting excited almost despite himself.
"No. I knew you wouldn't possibly guess." Snape said, looking smug.
Harry paced around the room for a few minutes, thinking hard. He was vaguely surprised that Snape let him move around like that - I mean, sure, Snape liked to pace himself, but he was the teacher. Finally, Harry shook his head, "Alright, I give up."
"Now, you did have something you wanted to talk with me about, Potter?" Snape countered.
"Yes, I wanted to ask if you wouldn't mind coming up with some more duties for Draco Malfoy." Harry Potter said.
"Oh?" Snape responded, "What kind of duties?"
Hrm. Harry thought furiously, having not really have thought about that before, "Maybe more patrols? Having him in the room during our... study sessions puts everyone on edge. And he's less likeable than most of the other Slytherins."
Snape nodded slowly, "And you'd really like to actually practice wandless magic with Miss Granger?"
Harry wheeled around, his bright green eyes wide as he realized that Snape had just admitted to something. Granted, it wasn't a big thing, or something that Harry hadn't expected, but still. "Erm. Yes, sir." Crap. then he knew about the stupid prank that Harry had pulled.
"On the contrary, that prank wasn't stupid at all." Snape said, and Harry started, belatedly realizing that Snape had simply responded to something that Harry was thinking. Man, that was totally creepy. "I always appreciate the chance to see how I am perceived from as many eyes as possible. It allows me to finetune the act, so to speak."
"So, you want people to think of you as mildly terrifying?" Harry asked, adding "Sir" on the end just to try and not sound so cheeky.
"If they didn't, do you honestly think the Weasleys would study at all?" Snape said. "Nobody takes Professor Sprout seriously, which is mostly fine. Herbology isn't generally a dangerous subject. Potions, on the other hand..." Snape looked grim.
"You've seen it, haven't you?" Harry prompted. "Potions accidents."
"Permanent ones, yes." Snape said, "Some even lethal. Others precipitated by me."
Harry was wide-eyed at that. Just staring at Snape. "You... you... what?!"
"Repeat that to anyone and you'll regret it." Snape said, his eyes sparkling, though his lips were pulled down into a scowl.
[a/n: I did mention Snape pranked people. Potions are his specialty, of course he'd have found "mostly safe" ways to use the Potions Lab for Mass Chaos and Destruction.
... yes, there were Good Reasons Lily didn't find Snape's pranks funny. What's another? He's too Slytherin to blatantly target the Marauders, so half the time Lily was in the midst of the devastation.
I'd be kinda pissed at my friend too.