spoil
Definitions
To diminish or destroy the value, quality, or character of something.
To cause a person, especially a child, to become demanding or selfish through excessive indulgence.
To become unfit for consumption or use, typically through decay or decomposition.
Examples
If you leave the milk out on the counter all day, it will surely spoil.
Grandparents often love to spoil their grandchildren with gifts and treats.
Don't let one bad experience spoil your entire vacation.