Katsuki was bold, it was obvious from his words to the way he walked; and it only became even more noticeable after Katsuki realized he had feelings for you.

He didn't have much, if any, knowledge about romantic relationships or how to approach the person you were attracted to in a normal way.

With his little, if any, knowledge about romance, he decided that the easiest and quickest option to show his interest was by flirting.

The problem, was that Katsuki was still Katsuki and since he had no idea what he was doing, it was easy for him to get nervous every time you flirted back.

He had no idea if you were teasing him or making him understand that you were also interested in him in the same romantic way, but it always ended the same way; with Katsuki and his cheeks red after flirting with you and you flirting back.