A phrase wich is used by somenone who is actually fine or some depressed people who don't wanna show their truefeelings
Example 1:
Person 1: Hey, are you allright?
Person2: Ah, yeah, I'm fine! What about you?
Example 2:
Person 1: Are you okay?
Person 2: Oh, don't worry about me, I'm fine. (Lie)
she is not feeling good (mentally and/or physically) and thinks you (S.O.) might tell her "I know you're not baby, what's wrong?" we may not tell you and might get annoyed if you keep asking but we may eventually tell you but we take your caring words to heart and it usually makes us feel better.
(S.O.): Hey, how are you love?
girl: I'm fine wbu
(S.O.): I know you're not baby, what's wrong?
girl: (explains problem)
(S.O.): Hey, how are you love?
girl: I'm fine wbu
(S.O.): I know you're not baby, what's wrong?
girl: You're right but I'm getting through it, thank you
(S.O.): Of course, let me know if you need ANYTHING
1Mostly used as a reply to “How are you?” Or “U ok?”.
2Under specific and varying circumstances it is used when the person who says it is trying to be passive-aggresive. Due to it’s commonality, it is ridiculed by the internet for being a cliche way to respond after an argument.