When a person has taken the moral high-ground or are just up themselves, they are being "Holier-than-thou". Holier-than-thou literally means, holier than me or better than me.
Just because I made one stupid mistake doesnt mean Britney gets to give me this holier-than-thou attitude!
acting like one is superior to others, condescending
I hate that bastard's holier-than-thou attitude.
Refers to someone that is stuck-up, or a snob. They must ALWAYS be the leader, and they are always a good leader. Ironically, they always have numerous faults, but never EVER admit to them.
Ryza from NationStates.net is holier-than-thou