Thick as a brick.
More Traditional Proverbs:
Far away is only far away if you dont go there.Traditional
Many an Irish property was increased by the lace of a daughter's petticoat.
Traditional
He that fights and runs away, may live to fight another day.
Traditional
The mother-in-law remembers not that she was a daughter-in-law.
Traditional
Better die than turn your back on reason.
Traditional
In water one sees one's own face. But in wine one beholds the heart of another
Traditional