The most sugary thing, with the most sugar in it.
Sugariest things are very sweet and might not be very good for you if you have too much.
Examples:
This is the sugariest candy I've ever tasted.
The sugariest drink is not good for your teeth.
She bought the sugariest cake at the store.
The sugariest food is not always the healthiest!
The sugariest dessert in the world is so sweet, it might make your teeth hurt.
The sugariest thing I've ever eaten was like eating pure sugar!