Answer on a postcard phrase
A straight and short answer, or an unnecessary one because it is clear to everyone.
Don't just give me answers on a postcard! I expect some more explanation and justification.
I always avoid giving answers on a postcard because I don't want to answer a lot more questions.
I expected a detailed answer but what I received was just an answer on a postcard.
The origin of this phrase is not clear.
Children or adults often say this phrase to get their friends to join in something, especially to jump into a swimming pool (pond, lake, etc.)
“Last one in is a rotten egg!” yelled Jane, jumping into the pool.