My dad had found some notepads at a joke shop (he loved those kinds of shops and Spencer's Gifts was his favorite), that he kept in his car and they said:
"do you always park like this or are you just being an inconsiderate SOB today?"
And he would slip those under peoples windshield wipers when they parked to close or blocked him in or something.
Maybe you could try that. Slip a note under the windshield wiper explaining that it makes it difficult to get out of your driveway and you sure don't want to run the risk of accidentally hitting one of their nice cars trying to maneuver out of your driveway when they park in the street.
Dont' make it threat like (I just read what I wrote and it did sound like a threat) but a genuine concern of : "i'm really scared I'm going to hit one of the parked cars trying to get out and I would NEVER want that to happen"
Some college age kids do not think about anyone but themselves. I know, I used to be one. But if you point out that other people actually do live in the world besides them, they are usually cool about it.