Two things- You can forget it. OR you can fuggedaboudit.
Here's the difference.
Forgetting is you put it out of your mind. Like it never happened. This is NOT, I repeat, NOT ignoring. In order to ignore something, you have to know it's there, you just pretend it isn't. Forgetting is erasing the incident completely from your mind.
Fuggedaboudit is a combination of forgive, ignore and forget. It's also a form of revenge. Anyone who can do this is a person you want on your side in a street fight.
Tomorrow, an example.