"Where are we?"
"In my mind. You are an excellent legilimens professor but I have had extremely through training in occlumency. I was aware of you almost from the moment you entered my mind. The oubliette is one of many defenses I have. It also has the benefit of allowing me to see the mind of the person attempting to see my mind."
"What happens now?
"I think I'm willing to say that we are even. You attempted to invade my mind, I invaded yours, although, actually, technically that not true since we never left my mind."
"You repulsive little-"
"Ah-ah-ah. No, Professor, I would be quite careful how you address me at this point. Technically you are still trespassing and I would be within my rights to leave you locked in the oubliette."
"Fine what do you want?"
"Mutual respect."
"As if I could ever respect a Potter!"
"You will find it is in your best interest to do so, Professor. There is a matter of a life debt between us. You owed James your life, that means you now owe me. There is the debt by how your actions resulted in the deaths of my parents, and there's the matter of your vow to Dumbledore."
"Why you little-"
"On a more personal note, or rather a personal observation, your life sucked as a kid, I understand what that can be like. But it is always in our power to choose our response to the lemons life hands us; by choosing our response we become responsible. Some choose to suck on the lemons they're handed and hold onto them until they are nothing but sour, bitter people, while others of us choose to temper those moments by focusing on the sweet things in life thereby making lemonade. Which are you?"
"What would a spoiled brat such as yourself know about loss or struggle or hardship? Let me out of here Potter."
"Fine, have it your way, but know this Professor I know everything about you. I know how you secretly hoped my father and I would die leaving my mother available for you. I know how you claim to love her. To you love equals ownership, an example you absorbed from your louse of a father no doubt. If you had gotten my mother how long would it have been before you started teaching her her place by knocking her around. Judging by your response to her aid fifth year my guess is not long.
"I am ashamed of how my father and his friends treated you in school. If it weren't for the fact I know Sirius regrets it, and the fact that my father let go of his rivalry with you long enough to do the right thing and save you from Remus I would be very troubled. You didn't deserve the way they treated you.
"This obsessive need of yours for revenge isn't healthy though. James Potter has been dead and buried for a decade now. Carrying out your grudge against him on me because I resemble him is just pathetic. Haven't you ever heard the best revenge is living well? You've accomplished lots, the youngest Potion Master in a century. Yet you still measure yourself by the yardstick of a dead schoolyard rival, it's pathetic.
"Shut up, Potter. You're too young to understand anything."
"Mutual respect Professor. You'll find it smoothes out lots of pathways. Continuing your animosity won't get you anything. If anything it will wind up costing you more. I'll leave you to think about it."
Snape almost broke again. He found a difference in his prison this time. He could think but only about Potter's words. Which was almost enough to drive one mad. The relief he felt when the boy re-entered was considerable.
"Are you ready to discuss terms, Professor?"
"Yes, yes anything just let me out of here."
"Okay, for starters I want a wizards oath from you to enforce this agreement. No digs, slurs or insults against me or my family, more specifically my father, godfather, and Uncle Remus. In your classroom and out, you will apply the school rules fairly and evenly to all students, no more taking points just because you feel like it. You will treat me and all the other students in your classroom with a modicum of courtesy, no degrading insults, however outside the classroom you may insult us to your hearts content but points and rules will still be evenly applied and removed from all the houses.
"Give me one reason why I should Potter."
"The alternative is staying here."