As a nuisance:
* The pest kept bothering me for candy, so I finally gave in.
* Mosquitoes are a real pest during the summer months.
* That pest of a dog keeps digging holes in my garden!
As an insect or other harmful creature:
* The farmer used insecticide to get rid of the pests in his fields.
* The fruit was covered in pests and had to be thrown away.
* The exterminator came to deal with the pests in the basement.
In a more informal, playful way:
* My little brother is such a pest sometimes, but I love him anyway.
* Don't be a pest and leave me alone!
The word "pest" can be used in a variety of contexts, so it's important to consider the tone and meaning you want to convey.
