John Kerry was very good at his job as Barack Obama's Secretary of State, at least if you understand that job to be what Obama wanted it to be: Negotiating awful international deals that are not in the interests of the United States.
And it makes sense that Kerry would be good at this. He detests America, and has demonstrated this ever since he slandered his fellow Vietnam veterans at the Winter Soldier hearings in 1971. John Kerry is an anti-American jerk and a terrible human being.
So it's not surprising that he would get royally pissed off about the voters rejecting his party and electing someone who would rip up one of the terrible deals he negotiated. Add in the fact that the someone ripping up the deal is Donald Trump, and you get a conniption fit like this: