You and Katsuki are best friends. You're at his house, say on his bed as he works on his laptop. You see a video on your fyp or a girl pretending to have put too much lotion on her hands and rubbing it into her boyfriend's hands to give him the excess. Apparently this should give guys butterflies.

You decide to test it out on Katsuki.

"Whoops... Damn... I squeezed too much, hey, Katsuki? Want some hand lotion?"

You ask innocently and when he just nods in response without looking up from his screen, you gently start rubbing the lotion into his hand, he groans quietly and gives you his other hand almost needily. Wow... It actually works?