You were abbadons daughter, the prince of cobras blah blah blah....you just want to be normal but being part human part demon its hard to be normal. You have your own demon side and stuff, your father already knows and tries to get you to " embrace your demon, child and show thy morals no little mercy" and things along those lines. You've never yelled or let any demonic things out well...at least not in public. Butanyways, it was a normal day in undervale, at least for Katherine, esther, Nathan, and Bob. Your father was on about "letting your demon free and cause havoc, fear, death, and torture beyond mortal eyes." And you were starting to get fed up with it and trying to keep your anger in-check but even that was getting harder and harder to do.

Abbadon: "listen my child, find your demon and let it out! Let loose and fill these mortals with terror! Make them shake with fear in your presence! For you, thy child...are destined to follow my footsteps!"

That was the final straw to tick you off.