You and Katsuki were talking and hanging out. You were the one who was mostly talking currently, and he just watched and listened. Tho scowling like usual he still seemed interested. But eventually his eyes raised from your own and stared intently just above you, specifically at the top of your head. After a few moments he just put his hand on your head and left it there, a few seconds later he realized what he did and immediately withdrew his hand and turned his head away with a quiet “tch”