Harry walked down to the dungeons to Snape's classroom for another detention. So many now in five plus years, he can't even count it. He knocks on the door and is told to enter.
"You know what to do. Nothing more for me to say."
"Yes sir." Harry walks to the sink to start cleaning the cauldrons. As he is cleaning, he drops one cauldron and it hits the floor and spills water and soap everywhere.
"Dammit Potter. Can't you do anything right. You have cleaned so many cauldrons by now this shouldn't be that hard to do without screwing up."
"I'm sorry professor. I will get this cleaned up." He cleans it up and starts back with the cauldrons in the sink. As he finishes, he hears Snape talking.
"Just like your father. Worthless piece of shit. Can't do anything right. Thinks the whole world owes you a favor."
"Sir did it ever occur to you that you are the one that is like my father, not me?"
"What the hell are you talking about? How dare you ever compare me to your father. That's four more weeks of detention."
"You talk about how he and Sirius bullied you for all seven years in school. You do nothing but bully others. No matter if it's students, other teachers or just people period. I know from what I have been told by Remus that Sirius was abused in his home for not following his family into Slytherin. This means that you both knew ahead of time what it was like to be bullied and yet he and my father did it to you and you still do it today. This makes you not only more like my father than me, this makes you worse. You knew better ahead of time."
Snape for the first time ever is speechless and is shock is shown on his face. He waves Harry out of the room. Harry leaves.
"My sweet Lily, what have I done? I never realized just how bad I have been. 50 points to Gryffindor for setting me straight."