i do not think that means what you think it means

kids told to get ready for bed and to go brush their teeth.

10yo:  DIBS ON BRUSHING TEETH FIRST!!!!!

7yo: [laughs while grabbing the tooth brush and running around with it]

10yo:  I CALLED DIBS.  DIBS IS 9/10THS OF THE LAW!!!!!

me:  [falls off couch laughing]