Well here is my suggestion:
When someone shoots you from inside a car then the car health starts reducing !!!
If he continues to db the car will burn automatically and shooting from outside will make the car burn faster!!!
That way he has to get out finally to fight on foot !!!
A good idea for the DB-er would be:
Create a platform to air or water somewhere somewhere somewhere far from GTA can not reach anyone without teleportation ..
NUB abusing a DB is automatically sent to that platform where she some time without being able to talk on chat or give / kill [automatically muted]. So nobody gonna give a DB or at least do it less often ...
Its just a idee