Saccharine

[Sarah]

An often derogative term for someone who is so [sweet], it's (almost) annoying. Used for people who are overly-optimistic, unflinchingly-kind, and innocent to the point of disbelief that anything bad happens to the world.

Not to be confused with [Saccharin], the artificial sweetener.

[Justin Bieber]

too sweet or too polite:

[Couch Potatoe]

Excessively sweet or sentimental.