If you are looking for genuine splendid sarcasm:
One of the beautiful people: wealthy or famous people whose lifestyle is usually expensive and well-publicized.
If you were to say "He thinks he's one of the beautiful people", you mean he puts himself in a class where (the little) people are expected to fawn over him and that he is faultless. (The faults of beautiful people are quickly overlooked by their adulators.)
(By the way, beautiful people can be taken positively, but it's easy to spot sarcasm with this phrase.)
(update)
Saccharine: cloyingly agreeable or ingratiating; exaggeratedly sweet or sentimental. Sickly sweet.
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There are also several words with a similar meaning (besides the ones already given) in common use. These all will universally be taken in negative terms:
priss: (back formation of prissy) An excessively proper person; one who is affectedly correct or prim. (where proper means conforming to established standards of behavior or manners; correct or decorous.)
prude: a person who is excessively or priggishly attentive to propriety or decorum; especially : a woman who shows or affects extreme modesty
victorian: having the characteristics usually attributed to the Victorians, especially prudishness and observance of the conventionalities.(mildly negative)
self-righteous: (adjective) confident of one's own righteousness, especially when smugly moralistic and intolerant of the opinions and behavior of others. (To call someone a righteous person, on the other hand, generally is a positive or neutral term suggesting their religious nature.)
If you want something is coarser language, there is this. (Don't look if you are a prude.):
He thinks his shit don't stink: He is so much better than everyone else. (ref)