What would be considered a “galactic screwup”?

Isaac Arthur is a popular YouTuber who explores different topics in futurism. He makes a new video every Thursday and he is amazing. In June, one of his episodes is called “Galactic screwups”. I love looking at his Google Doc and guess what he is going to cover based on the title. Yet the “Galactic screwups” one is stumping me. Isaac often talks about highly advanced societies employing gamechanging super-advanced tech that can alter the universe on a grand scale. So basically, their is little to nothing “impossible” on Isaac’s channel. What do you think he will cover in “Galactic Screwups”? My theory is that he will cover stellar engineering projects that may go awry and wreck planets or stars but I would like some other opinions on obscure hypothetical mistakes future humans or aliens might make.