Sightseers (2012)

Tina decides to go away on vacation, much to the dismay of her overbearing manipulative mother who has never forgiven her for the accidental death of the family dog.  Boyfriend Chris, a writer, has a trailer they can use for the road trip, and a list of attractions  they must see.

After mom is unable to guilt Tina into staying home, the happy couple head off on their journey. But at their first stop, Chris and Tina get irritated by a man who throws his trash on the floor and refuses to pick it up.

Later as they're leaving, Chris backs over the man with the trailer.  Tina is horrified, but not enough to stick around until the policy arrive or call an ambulance.  As their trip continues, the dead bodies pile up and things keep getting more desperate.

This is a black comedy, and there are a few disturbing scenes.  I think sometimes I expect too much humor from a black comedy. It's okay but not a lot of laughs.  None of the characters are likable, which means sometimes the killers and victims are both so unlikable that you don't care if they all die.