Regardless of where we stand on Brexit, surely we can agree that there is a need to be civilised about the process? Some of the leavers at present appear to think that threatening the EU will get them what they want.
It perhaps says something about British business; my (10 year old) experience was that what was increasingly valued was to decide what you wanted and to be as obnoxious as possible to get it, trusting that the other (weaker) party would give in, as something was better than nothing. I suspect that this works for moderately large companies, so supermarkets can treat suppliers that way, but very few suppliers are big enough to treat supermarkets that way.
When it comes to Brexit, the question is which is the stronger party? Those threatening the EU, or expecting them to change their mind at the last minute appear to think we are.
That said, I think the underlying assumption that we can bully our way into a good relationship is practically and morally wrong.