Expressions can be funny things. An idiom is a term or phrase that is intended to be descriptive, not literal. Calling someone "butterfingers" or stating that they have butterfingers generally indicates that the person is clumsy.
The term "butterfingers" suggests that the fingers are slippery thus causing one to handle things awkwardly, drop things, miss a catch, or to use another idiom, be “all thumbs." Using the term clearly does not mean that someone literally has butter or any other slippery substance on his or her fingers. It is often used jokingly, as a reference, when a person drops or nearly drops something. The term may be directed toward another person, or someone finding himself suddenly clumsy may use the term for himself or herself.
Such terms are frequently used to laugh at one’s own minor mishaps, as a self-deprecating bit of humor. Rather than giving in to embarrassment, a person can make light of the situation by tossing out the term "butterfingers." Situations arise frequently in which this idiom would be appropriate, from failing to catch a ball to watching as an item slip through a person’s fingers. If the dropped item breaks or causes a spill, it is even more likely that such a term would come into play to ease potential tension. Others may use this term in a genial way to help someone else laugh off such an accident.
This particular idiom may have emerged from the baseball world. It has commonly been used to describe someone who misses a fly ball or who misses or drops a catch that would have resulted in stopping another important play. It is also used in other sporting events to refer to missed catches, such as a missed pass or a fumble in football.
Idioms and slang terms can be rather confusing at times for people who do not share a common first language. English terms such as "butterfingers" may be confusing to those just learning the language. Of course, the same is true of various other languages, and there are a number of words that may not make much sense if translated literally. Attempting to use such terms literally via translation can also create a humorous situation, and may lead to further idioms.