Related to the saying, An apple a day keeps the doctor away. This is said to sick people. So in saying Have an apple you are wishing that they recover soon. Example: (John is sick in hospital. Bob enters.) Bob: How are ya? John: Bob, I'm in the hospital. I'm sick! Bob: Have an apple!
HAVE AN APPLE.
Meaning of HAVE AN APPLE. in English
Slang English vocab. Английский сленговый словарь. 2012