I noticed something on a rewatch

In the first episode, Korosensei is being tailed by a fighter jet which he later cleans.

The jet in question appears to be an F-22 Raptor, the top speed of which is about Mach 2.5. That's an eighth of Korosensei's top speed of Mach 20.

He was **letting** that jet tail him for shits and giggles.