It would be best to use a permanent marker if only to make the prank go on that much longer before it finally faded and washed off the swordman's face.

"I bet I could if I tried." He refuses to have his mind changed as well, and it seems he will stubbornly believe he can change Gokudera's.

"Now now, Gokudera, it wasn't" Oh shit, he should not have shut his eyes. He suddenly as a chest full of Gokudera grabbing his shirt, and oh, there is sand, and he is laughing so hard he can't finish his sentence. Yamamoto's fingers dig at the sand under his head, bringing up a handful, he will aim to return the favor, who knows maybe while he is dropping the sand down Gokudera's shirt, he can find that lighter too.