If I was to guess what it would mean; if you said, "You have the life of a boiled fish."
I would say it means:
You have no life. ~This is another Idiom; since, it is impossible to not have a life.
In my opinion, you don't have a life worth living. ~This is basically what someone means when they say, "You have no life."
You have a painful life. ~Depending on if the fish is still alive or not....
Your life is tragic.
You have a hard life.
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Idioms are another way for people to feel special. They allow us to create or say something, that not everyone can decipher. We are free to do whatever we want; so it is a choice between: being easily understood or feeling special.