[Linus Gump]

I wouldn't recommend hitting them, that will open up a can of worms you don't wnat to deal with. It becomes road rage, and since all the cop is going to see is your vehicle parked on top of thiers, guess who they are going to think is the aggressor? I drive a semi all day, one loaded with gasoline at that, and morons do this to me all the time. I understand your frustration with it, but you gotta keep your cool. Defensive driving teaches you to yeild your space to prevent an accident, and to expect that the other driver will do something unexpected.
Merging is one of the biggest complaints I currently have about driving. It seems there are very few driving schools that teach how to properly merge, and who has the right of way at a merge point. Mommy and Daddy generally don't teach their kids either, mostly because they don't know themself.
The person on the freeway has the right of way, and the person merging is responsible for matching thier speed to that of traffic on the freeway. The merging traffic needs to be up to speed as quickly as possible and positioned so as to blend into traffic without causing traffic on the freeway to alter their speed or change lanes. They need to merge as early as possible, and not wait until thier lane ends to merge. Trucks and anything pulling a trailer, or vehicles that are obviously going to be slow to get up to speed require traffic on the freeway to allow extra space for them to merge.
Anytime I see someone following these rules, I make every effort on my part to ensure a smooth merge for them. The ones that dont usually wind up driving on the shoulder for a while before getting on the freeway and then speed past while flipping me off.