"thoroughly rotten" is correct and usable in written English.
You can use this phrase to describe something that is in a very bad or disgusting condition, or to describe someone who is morally depraved. For example: "The food looked thoroughly rotten; we decided to leave the restaurant right away!".
"It is a thoroughly rotten system that is trying to defend itself against civil society here.
IT DIDN'T PURR To make matters worse, the first XJ40s were thoroughly rotten cars.
"Poorly controlled, despite the notorious power vertical, it's thoroughly rotten, and therefore allows for operation of these leaky washtubs".
The Rock, a thoroughly rotten character, is short for his former nom de mat, Rocky Maivia, a nice guy who finished last -- like Michael S. Dukakis.
But in a place like the Goodwill store in East Harlem, all it meant was that the economy had gone from thoroughly rotten to merely terrible.
If the West Countrymen are to salvage something from a thoroughly rotten September – two flaccid displays on the road, one scratchy victory over Leeds at home – they must win, and win well, against a peculiarly inconsistent Wasps side this afternoon.
Having collected a suitable variety and quantity of apples (10kg will easily produce enough juice to fill a demi-john) you will need to wash them thoroughly, remove any rotten bits and cut them into quarters.
The dry soil was thoroughly mixed with well rotten cow dung.
"We've had very few problem guests, because everyone is thoroughly screened, so not many rotten apples slip through.
Make sure your bamboo is thoroughly seasoned and is not split or rotten.
Poor Bella, what rotten bad luck - but the good news is that Edward is a thoroughly decent vampire who courteously skips class when they're analysing blood samples.
