For me it really depends not only on the game, but what's going on inside the game at the time. If I'm just driving along from point A to point B, I don't usually make it a point to ride the sidewalk and mow down as many people as possible, just for kicks. However, if I'm on a mission or in a shootout and people get in my way, then any previous boundaries go out the window. If you're in my way, then you're dead.
The same applies for dick-headed pedestrians or drivers who hit you while you're trying to cross the street. If I'm running through an intersection in SR2 and someone bumps into me, they are getting an Annihilator rocket up the ass, guaranteed.
In sum, I don't know if I fit into any category neatly. I just go on about my business, but God help you if you get in my way.