Responsible parents teach their children to be good sports in victory and defeat. But some prominent adults apparently didn’t learn that lesson.

And while it’s understandable that many politically minded Americans are either a) down in the dumps, or b) riding on a cloud over Tuesday’s presidential-election outcome, they should put reasonable limits on their glumness — or glee.

Then again, Donald Trump is not a reasonable man. Last year, the billionaire blowhard and host of NBC’s “Celebrity Apprentice” carried the “birther” nonsense about President Barack Obama to a ridiculous degree.

And on Tuesday night, he carried on to embarrassing lengths as the reality of that U.S.-born president’s re-election sunk in.

Among the ranting tweets issued by “The Donald”:

“The world is laughing at us. ... We can’t let this happen. We should march on Washington and stop this travesty. Our nation is totally divided!”

When assorted news outlets declared the president the victor Tuesday night, Mitt Romney was still leading the popular vote. That prompted this irate Trump tweet: “The Electoral College is a disaster for democracy.”

President Obama did eventually win the popular tally by, as of Wednesday evening, about 50.4-48.1 percent — a margin of more than 2.8 million votes). He rolled up big, late-arriving numbers in the Democrats’ West Coast strongholds.

That convergence of electoral and popular-vote winners was likely of no consolation to Mr. Trump.

But while that hissy, sore-loser snit from “The Donald” was unseemly, the sore-winner “analysis” of MSNBC commentator Chris Matthews was downright appalling.

Mr. Matthews echoed the dubious notion that Hurricane Sandy was an upward turning point for the president. According to that theory, Mr. Obama’s post-Sandy visit to New Jersey, where he was effusively praised by Republican Gov. Chris Christie, cast him in a positive, bipartisan light.

Caught up in the giddy afterglow of Tuesday night’s triumph, Mr. Matthews said: “I’m so glad we had that storm last week.”

After a voice in the background went “ooo” at that callous observation, Mr. Matthews added: “No, politically I should say — not in terms of hurting people. The storm brought in possibilities for good politics.”

The storm also brought in natural fury that killed more than 110 people in the United States, most of them in New York.

Mr. Matthews tried to “clarify” his comments Wednesday by — what else? — tweeting.

Yet the repugnant damage was done.

Yes, these are extreme examples of taking political zeal too far.

However, they are also reminders that in our self-governing system, we all should exert some self-control lest we get too down — or too up — over election results.

Victorious President Obama and vanguished challenger Mitt Romney both gave gracious speeches very early Wednesday morning to mark the end of an often-bitter political season.

And while we live a divisive era of perpetual campaigns, that election is over.

That means the winners and the losers should call a political truce — at least for a few days.