We already know that Tony Stark loves making pop culture references. However, it looks like Iron Man's most recent reference actually confirms that the Man of Steel exists in the Marvel Universe.
Marvel has just released a preview from the new comic book Tony Stark: Iron Man #13 which was written by Gail Simone and illustrated by Paolo Villanelli (via ScreenRant). In the preview, Tony admits that he does have a weakness, which happens to be metaphysics. However, since this is Tony Stark we are talking about, he does so in the most awesome way possible.
In the comics, Tony has a strange confession. "I am smart. Really smart. But it's a focused, narrow thing in a way. I see a problem, I blast it or buy it or give it robotic shoes. Metaphysics? That's my kryptonite," he admits.
Yes, metaphysics is Iron Man's kryptonite. It's an awesome nod to Superman and the only thing in the universe that happens to be Kal-El's weakness. Of course, the term "kryptonite" has already been added by Merriam-Webster in September 2018 so it is a real word. Nevertheless, it's great to see that Tony has no problem making a reference to the DC Universe.
The description for Tony Stark: Iron Man #13 reads as follows:
Tony Stark: Iron Man #13 will be available starting June 19.
Related: Iron Man Movie Writers On Tony Stark's Fate In Avengers: Endgame