Spider-Man: Oh, no! You have found my weakness. Small knives!
Peter Parker: We all have secrets: the ones we keep... And the ones that are kept from us.
Gwen Stacy: How did you get up here?
Peter Parker: The fire escape.
Gwen Stacy: That's twenty stories.
Peter Parker: Your doorman's intimidating.
Peter Parker: I've got to stop him, because I created him.
Gwen Stacy: That's not your job...
Peter Parker: Maybe it is.
Peter Parker: Ahem, you know, if you're going to steal cars, don't dress like a car thief.
Car Thief: You a cop?
Peter Parker: You seriously think I'm a cop in a skintight red and blue suit?
Dr. Curt Connors: Do you have any idea what you really are?
George Stacy: Thirty-eight of New York's finest, versus one guy in a unitard.
Answer: If you're talking about after the dunk scene, Ben didn't see it as Peter standing up for himself. Instead, he says Peter humiliated Flash and then finds out he's the same one that punched Peter earlier. So in Ben's mind, this was retaliation or retribution, which is not OK.
Bishop73