1.
If you cut something up , you cut it into several pieces.
He sits in his apartment cutting up magazines...
Halve the tomatoes, then cut them up coarsely.
PHRASAL VERB : V P n (not pron) , V n P
see also cut up
2.
If one driver cuts another driver up , the first driver goes too close in front of the second one, for example after passing them.
They were crossing from lane to lane, cutting everyone up.
PHRASAL VERB : V n P