I was watching a sitcom and here is this part of the script.
A: Okay so what's the problem?
B: It's...I can't explain it.
B: It's.... ineffable.
A: I am not "F-able"?
B: No, no, no, no. Ineffable, ineffable means it can't be explained
For your information, A used to be B's girlfriend (B dumped her) and a few years later B wanted to meet her again and they have become a couple again. However, again, B doesn't want to go out with her for some reason and tries to say her that they aren't meant to be or something.