Final answer:
Benny was upset due to the significance of the Alterna-Fiesta as a personal and collaborative project that showcased their unique interests and was a form of self-expression.
Step-by-step explanation:
Benny was mad about Malú wanting to cancel the Alterna-Fiesta because it was something they were both looking forward to and had put effort into planning. The Alterna-Fiesta was meant to be an alternative celebration that reflected their own style and interests, differing from the traditional school events. Benny likely felt frustrated or disappointed that Malú wanted to cancel an event that was important to both of them and may have represented more than just a party, but a form of self-expression and belonging.