that's just not on - meaning Here is some context (It`s from English at work, BBC series) Anna: Well, speaking personally, I don't think she's pulling her weight. She doesn't seem to do any work and just keeps going out to buy cappuccinos. Paul: Well, that's just not on. Look Anna, I will look into this straight away and see if I can sort this out. Thank you for bringing it to my attention. Now, I think you've earned a custard cream Everything seems to be clear except one phrase. Paul said: "Well, that's just not on" how I should understand this phrase? What is the grammar? Could you explain, please? Extra examples of use would be nice too.