You shouldn't just cut people off without warning.
Steve is driving on the freeway in heavy traffic and realizes that he's in the wrong lane to exit.
Steve wants to change lanes.
Steve sees an opening in the lane and signals, waiting for the person to allow him in.
Steve sees an opening in the lane and veers into it before someone else can take it, cutting off another car.
The person slows down a bit to make space for Steve to fit in.
The driver who is now behind Steve is infuriated and swears at Steve from his window.