Answer:
His holier-than-thou attitude seemed rather unchristian.
Step-by-step explanation:
The adjective holier-than-thou is used to describe someone who thinks that they are morally superior to everyone else.
Adjectives are words used to modify nouns. Adjectives that consist of more than one word are called compound adjectives. Words that make up the compound adjective have to be connected by a hyphen (or hyphens in cases when the adjective consists of more than two words). This also applies to the adjective holier-than-thou, which is here used to modify the noun attitude.