In my opinion, this goes by the local minhag. In NYC, the minhag is to bump, because people park so close to each other that you need to. In most other communities, it is highly frowned upon.
I assumed we were talking NYC
In NYC, the people with the fancy cars take up 2.5 parking spots, and the people with the driveways take up 2 parking spots. One for their driveway and one for their car.
So no wonder everyone else around them has no choice but to play bumping cars.