Tomura Shigaraki:

You just got curious if the hand would fall off, so you slapped the back of his head. You and him stared as the hand that was on his face had now fallen on the floor. When he slowly looked at you, you knew you had to run so you did.

Kurogiri:

You tried but your hand appeared out of a warp on the other side of the room. As you stared at it, he asked you in a "how dumb are you" tone what you thought would happen before he stepped away. When you pulled your hand out the warp, he closed it before rubbing the back of his head, now having a weird sensation.

Dabi:

He was bored during a mission so he began flirting with you, so you gave the back of his head a soft slap, telling him to stop it and focus. He just chuckled in amusement and rubbed the back of his head.

Himiko Toga:

You were both bored on the sofa, when she suddenly slapped the back of your head. You just did it to her as well. So you both kept slapping each other's heads. Eventually she stopped and groaned, saying this is also boring.