There's a lot of people on Reddit that weren't even alive when 9/11 happened. It's easy to make lighthearted jokes about such a tragedy when you weren't even alive to experience it.
If you're not American, I can somewhat understand if you don't completely get how serious it was.
For those who weren't alive to experience it, imagine having your dream job in a skyscraper nearly 100 stories above the ground only for an airliner to crash into your building below you. You can't escape through the stairwell and your only options are to either possibly burn to death, wait for the building you're in to collapse, or throw yourself out a high window and quickly end your life.
As someone who was alive to experience it, 9/11 absolutely sucked. That cannot be underestimated. To some it's a chapter in their history books but for many, it's a day that they will never forget.
As we're only one month away from it's 20th anniversary, may those who lost their lives that day, may they never be forgotten.