Because he's angry that he lied (so he wants to punch him) and/or because he got triggered = horny or he felt something when he heard him say that he lied BECAUSE he wanted to sleep with him in the first place. (But yeah
^Valid points. Or maybe the way pyeonghwa absolutely dominated him during that blowjob still stings his pride. He wants break pyeonghwa the same way (?)
Sense of pride probably bc he's never failed to perform well in his tasks that his superior gives him, and frustration so he's gonna try taking it out sexually now ig LOL
depressing to see that the teach feels the need to use his body now for survival