Litter

When there are no litter bins in an area (or if existing litter bins or full or broken) guests will throw their leftover food containers, papers and bottles on the ground as litter.

Problems
Litter can become a major problem in parks that are short on handymen, and it can also be problematic to the happiness of your park guests. If there is too much litter in your park or in a certain part of your park, guests will become unhappy and will begin saying, "The litter here is really bad." in their thought boxes. This will also greatly lower your park rating.

Angry Guests / Vandals
In Roller Coaster Tycoon 1 and 2, Litter is also the leading cause of angry guests, also known as vandals. When a guest walks through too much litter in a large amount of time, they will gain the special Angry emotion, which is characterised by a red, enraged face overlaying any normal emotions in the guest's window. While angry, guest will seek out objects to vandalise, such as benches, lamp posts and trash cans. Vandalism can be prevented with a well-placed security guard in areas containing the aforementioned items, although it is still recommended to assure that every section of your park contains a handyman to clean any litter, preventing these vandals from appearing, and it is recommended to place many trash bins near food stalls and bathrooms.

(This also applies to vomit.)