Minor disagreement (4)
(Other definitions for spat that I've seen before include "Reacted contemptuously" , "Bickering" , "A minor dispute or row" , "Slight quarrel - ejected saliva" , "Made gesture of contempt" .)
(Other definitions for tiff that I've seen before include "Quarrel (colloq.)" , "pet" , "Slight argument" , "Hard to lose opening argument" , "Mild quarrel" .)