As fit as a butcher's dog British slang
In Viet Nam, people often say that 'as strong as an ox' , and It is the same meaning with this.
The phrase 'as fit as a butcher's dog' means a person who is strongly fit and healthy even in the difficult situations.
He's as fit as a butcher's dog, although he works outside in cold weather for hours.
He is as fit as a butcher's dog because he always do exercise everyday.
The reference to the dog of a butcher is to a dog that would be assumed to be fed from garbage very well. It is not clear why this is considered to embody health, as it might be considered more likely that the dog would be overweight than fit. John Camden Hotten, Cant and Vulgar Words, in A Dictionary of Modern Slang, 1859.
People tend to like forbidden or illegal things just because they are forbidden or illegal.
He must have believed that stolen fruit is the sweetest, and he, therefore, cheated on his partner.