Well, the Berlin Wall opening was caused by the press speaker of the GDR government accidentally claiming that the border was to be opened immediately. Also, the man (Günter Schabowski) was one of the "Wendehälse": people who opportunistically condemned the GDR, socialism and all its aspects to gain the praise of liberals after the government fell in spite of having been in high political positions as early as 1978.

The most memed one (at least stateside) has to be (CW: homophobic slur) this baseball one. Not really catastrophic for anyone besides him, though. The Diamond Joe "this is a big fucking deal" incident is more well known but it doesn't come with a copypasta-ready apology and also didn't really matter.

edit: scrolling through the hot mic Wikipedia article and there are a few fun ones in there:

On 14 August 2008, actor Ernest Borgnine was interviewed on Fox News when he was asked about the secret to his longevity. Laughingly Borgnine responded "I don't dare tell you," but then leaned over to whisper into the ear of his interviewer, but the whisper was caught by the microphone; "I masturbate a lot."

On 2 March 2009, footage of Dutch news anchor Eva Jinek asking whether to loosen another button on her shirt (which might reveal too much of her cleavage) right before a broadcast, while muttering and shouting mild curses in both English and Dutch, was accidentally leaked to and spread on the Internet. She exclaims "Yeah, boobies!" at one point, continuing with, "Mother of God. Yeah, if you have it, flaunt it!" and citing her mother who might tell her: "I can see your breasts!" She responded the next day, saying she was not annoyed nor embarrassed by the leaked video.

In 2005, French President Jacques Chirac was heard criticizing British cuisine to Russian President Vladimir Putin and German Chancellor Gerhard Schroeder, saying "The only thing that they have ever done for European agriculture is mad cow disease" and "You can't trust people who cook as badly as that." He was also heard criticizing haggis, saying "that's where our problems with NATO come from", and that British food was the second worst "after Finland".

lol this isn't a matter of international politics but when i was in school for audio engineering we were in one of the classroom studios and me and one of the other students i was friends with were setting up a mic that the rest of the class in the control room had already cranked the gain up and i didn't know so i was talking mad shit about this other kid that had it out for me that I was getting increasingly tired of and I heard click "hey... uh.. the mics on" come out of the headphones nearby. Walking out of the booth was so awkward

not a hot mic, but Ratner gaffe is funny.

He said: "We also do cut-glass sherry decanters complete with six glasses on a silver-plated tray that your butler can serve you drinks on, all for £4.95. People say, 'How can you sell this for such a low price?' I say, because it's total crap."

He added "We even sell a pair of gold earrings for under £1, which is cheaper than a prawn sandwich from Marks & Spencer. But I have to say that the sandwich will probably last longer than the earrings."

After the speech, the value of the Ratner group plummeted by around £500 million, which very nearly resulted in the group's collapse. Ratner hired a chairman in an attempt to stabilise the situation, and was dismissed by the new company chairman in November 1992. The group changed its name to Signet Group in September 1993.

the world wasn't ready for him

Reagan's "we begin bombing in five minutes" has to be up there

On the May 24, 2014 episode of Tucker Carlson Tonight I audibly farted and shit myself a tiny amount which started the chain reaction that lead to fox settling a $700 billion lawsuit

Wasn't Romney's 47% quote one of these?

Not catastrophic, but a funny hot mic adjacent moment was when the voice of the Lotus on Warframe flubbed a word and accidentally boasted that 26 million registered losers play Warframe.

https://www.youtube.com/watch?v=VPytOVWZSqY

:TennoWhat:

It's gotta be this one, right?

In the decades before 2016, Trump's hot mic incident would have been lethal to any politician. It doesn't seem like much in hindsight because he ended up winning, but the Republican party was panicking and scrambling for an alternate candidate.

In a way, it ended up creating a lot of the political climate in the United States today. Republicans realized doubling down often was a viable strategy and have done it ever since. It also added to Trump's mystique, that he could buck the established norms to such a degree, that it convinced many chuds that anything was possible if they were a big enough asshole.

It was probably a major source of my radicalization, because the fact that he won in spite of it lead me to believe that optics were not the only thing going on with politics. It made me pay attention and figure out why this would happen and why it didn't matter.

"Major League Asshole" was big for a while: https://youtu.be/M8w7Yz1Htz4?si=I2u3tFeKARfqHeZW , but it clearly didn't derail Bush's campaign.

Gordon Brown calling Gillian Duffy a 'bigoted woman' might be up there. Not sure how big a difference it ultimately made to the 2010 election in the UK, but was definitely a flash point and you could see it as typifying a lot of the dynamics of the next 10 years

Trent Lott