litterbug
A person who carelessly throws trash on the ground.
A litterbug is someone who carelessly tosses trash on the ground instead of putting it in a proper waste container.
You've probably seen litterbugs in action: someone drops a candy wrapper on the sidewalk, tosses a soda can out a car window, or leaves a fast-food bag on a park bench. When many people act like litterbugs, parks become unpleasant, streets look shabby, and animals can get hurt by eating or getting tangled in discarded waste.
The opposite of a litterbug is someone who carries their trash until they find a proper bin, or even picks up litter they find along the way.