The sanctimonious person sounds like a hypocrite when he preaches to a friend about the evils of drugs, while he drinks one beer after another.

Sanctimonious is a twist on the words sanctity and sacred, which mean holy or religious. A sanctimonious person might think he's holy, but their attitude comes across more like "holier-than-thou." Though sanctimonious people might try to act like saints, their actions are far from pure or holy, which just makes them sound like hypocrites.

Definitions of sanctimonious

adj excessively or hypocritically pious

“a sickening sanctimonious smile”
holier-than-thou, pharisaic, pharisaical, pietistic, pietistical, self-righteous
having or showing or expressing reverence for a deity