I keep seeing this post going around so, for folks who want to know why not, here's a chemist's hypothesis:
-Human saliva has an average pH of ~6.7 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3800408/), which is pretty neutral.
-Monster energy has a pH of ~2.7 (https://patientconnect365.com/DentalHealthTopics/Article/Energy_Drinks_and_Your_Teeth_Should_You_Worry), which is quite acidic but not dangerous, except to your tooth enamel if consumed in large quantities.
-Rainbow sour belts contain malic acid (a common food additive as a potent acidifier and sour-flavor agent), citric acid (another common sour flavoring in pretty much everything) as well as ascorbic acid (aka vitamin C, used here mainly as a preservative). (https://candypros.com/products/sour-belts-bulk-rainbow)
-All of these acids when added to water would normally release their protons (H+ ions), thereby making the water solution more acidic. However, a chemical constant of these acids called the acid dissociation constant (pKa for short) indicates the pH of a solution at which acids are most likely to keep or release their protons. The pKa's* of these acids are higher (3.4, 3.1, and 4.2 for malic, citric, and ascorbic acids respectively) than the pH of the solution (2.7), which essentially means that the acids can't release their protons and all that acidic potential is trapped in the solid formulation of the candy.
-There's also some evidence that sugar decreases the solubility of acids in water solutions (https://pubmed.ncbi.nlm.nih.gov/3411471/ only sorbic acid is discussed here but it's relatively structurally similar to the acids in discussion). The undoubtedly high sugar content of both the Monster and the candy therefore may contribute to the accounts of the sour crystals bubbling/floating on top of the solution instead of dissolving.
-Malic acid in particular is notorious for causing mouth irritation when eaten in high quantities.
-Thus, I can imagine that upon consuming the battery acid spaghetti, not only is the mix itself quite potently sweet/sour, but also the solid malic acid coming into direct contact with your mouth quickly becomes painful, and as the solution mixes with your (pH neutral) saliva the trapped acidity of the malic/citric/ascorbic acids is dumped into your mouth and esophagus, creating a sensation that I can only imagine is similar to consuming actual battery acid (pH = 0.8).
(*Each of these acids actually has multiple pKa's corresponding to number of protons they're able to donate, but really only the lowest pKa is useful here since once that one dissociates then all of the other ones are already dissociated too.)
