Finning is when a person excessively gets mad over a simple subject. It usually results in the throwing or tipping over of the nearest object.
The word and definition is derived from "Fin", a nickname of school mate that would get mad over the simplest thing and go completely nuts for about ten seconds.
Danna and Cristian are at lunch.
Danna: Cristian, you are so stupid!
Cristian: (breathing heavily)
WHAT? DID YOU JUST CALL ME STUPID?!
*picks up banana and throws it at Danna*
Danna: OMG! Cristian, stop finning!