Former Prime Minister Kevin Rudd wants

to be Secretary-General of the United Nations but the present government will not nominate him. 
He was backed by former diplomat Richard Woolcott and a former government minister, Brendan Nelson. His  own party backed him. The present Foreign Secretary backed him.
Or did they? They said the right things perhaps. You don't upset Mr Rudd if you can avoid it. He has been known to lose his temper.
He would be a disaster as Secretary-General. It is perhaps one of the worst jobs in the world, presiding over a highly dysfunctional international organisation.
Of course some people would say that this is why Mr Rudd is suited to the position. He presided over a dysfunctional and chaotic government. It should not have been dysfunctional and chaotic but it was.  It was so bad and his personal popularity was so low he got tapped on the shoulder by Julia Gillard and, for a short while, we had a more competent leader. But, politics is politics, and Mr Rudd undermined her - eventually achieving his aim of getting the job back again. He lost the election.
The position requires a cool head, a calm demeanour, the ability to speak fluently while thinking on your feet, and diplomatic skills of the highest order.  
Mr Rudd is known as a diplomat - but for none of those reasons. He is a highly intelligent man. He speaks Chinese - although not as well as he believes he does if our Chinese neighbours are correct in their assessment of his ability.  He has a temper, he can show emotion at the wrong time, he isn't a fluent speaker - just a long winded one. Above all, he is not a diplomat. 
I know people who worked for him. They said he was often abrasive and impatient. He could be downright rude. He didn't listen. 
Mr Rudd has a high opinion of his own abilities. That may or may not be a good thing. His own party tore him to shreds and only reinstated him when they thought they were going to lose the election without him as leader. Now of course they have been talking him up and saying how suitable he would be for the role. They will criticise the government for not nominating him. 
I suspect many of them will privately be breathing a sigh of relief the government has refused to do so.