define "go off"

the weddin' was super duper, thanks-fer-askin'.

In case you're curious, I did not visit the library in Key West while there drinking rum, lying on the beach, petting Ernest Hemingway's grand-cats and eating key lime pie. I'm sure it's a cute library.

Anywho, plenty of fun moral dismemberment went on while I was gone.
Librarian: Mam, if you're waiting to use a computer, you cannot lean over everyone else's computer while they use them. 
Patron: I'm just waitin' for my friend to be done.
Librarian: Then you need to wait somewhere else

patron does not move, but just keeps looking at everyone else's computer screen. Poor, Children's librarian is looking her, not sure what else to say to this girl to make her understand. She then told the girl that she needed to leave the building when the girl finally said to her:
Patron: Bitch, if you keep starin' at me, Ima go off!