I've been better
A response to the question, “How΄s life?”
A response of “I’ve been better” can mean the person is not feeling well physically in various degrees.
It can also mean the person isn't feeling well emotionally.
It can be a low-key way of letting it be known that things are not so good without launching into complaining.
The person asking the question in the first place can decide whether to ask for more information sympathetically, or,
based on the responder’s tone, to leave the subject alone after sympathizing.