Flash is the act of expressing anger or annoyance by somewhat randomly snapping at someone.
Flash back is the act of flashing at a person who just flashed you.
Slang may or may not have originated in Sacramento (cousins there shared it with me).
He totally flashed at me today. See how it went down:
Person 1: Do you want to get pizza or tacos?
Person 2: . . .
Person 1: Do you want to get pizza or tacos?
Person 2: . . .
Person 1: Hellooooooo! Earth to Person 2! I said do you want to get pizza or tacos?
Person 2: Would you shut the f*** up? Can't you see I'm on the phone?!?!?! I couldn't care less about f***ing pizza or tacos. (flash)
Person 1: And I couldn't care less about you!! I'm out. (flash back)
“Flash” is another term that originated from rock climbing. The term “flash” is used to describe a flawless climb. A climber can say that they flashed a climb if they went from bottom to top without hesitating or taking any falls.
I just flashed that 5.11 climb, did you see that? I’m the man!