Yeah, I do know that it foreshadows the last part of the same chapter. What I was trying to say is that at the back of my mind, I'm always wondering if those lines were actually "double foreshadowing." As in, both foreshadowing the end of that chapter, and also some other event that we haven't seen yet.
Admittedly, this manga focuses on the comedic side of things, rather than the drama that is so common in Seo's previous works. Fuwa's "Curse you... I'll never forget what you did" will probably be played off for laughs when he fails miserably at his next attempt at ruining the Familia, but a small part of me always worries, what if Fuwa doesn't fail next time?