Short Answer
To answer a question without wanting to give any background information usually due to shame. Also used when you know the complete answer is extremely unexciting.
Ryan- Hey Brad did you sleep with that chick last night?
Brad-Short answer? Yes
Ryan- Long answer?
Brad-Yes.. and she turned out to be a "he" so lets drop it ok...

How was the movie last night?
Short answer? It sucked.