The real answer should basically say that you need to start negotiating.

Of course you need to be nice and civil (read Dale Carnegie's book) but also understand that you don't need to liked by some people. For negotiating there are many books. But the point is basically very simple: 1) figure out what you really care about, 2) learn what other side really cares about, 3) be nice, 4) every negotiation needs to end with both parties satisfied, 5) "no deal" is also possible outcome