There are so many ideas here, I think I'll have to write them down and eventually write a system of experiments on Sues using all of these.

Again, thanks!

I know it doesn't really fit what you were asking for, but that was my first thought. Gritter is what you sprinkle on a canon to get a darker, edgier version. If it's an official version you have a 'gritty reboot'. (Nolan's dark Knight films are the epitome of this.) In fanfics, Gritter can be used to create a 'Dark AU'.

A while ago, I beought up the concept of Logic Water and Crystals of Plausibility. Logic Water is like water except that it glows bright blue. When consumed, for Non-Suvians it has them think logically. It generally calms the consumer down. But if the consumer is Suvian, they will get SOCS and or disolve into glitter. Logic Water isn't foolproof; some Suvians might be immune to its effects. The Crystals work the same way, but thsy have a repelling effect.

As for their taste, I figure you'd have to combine the two. Perhaps you could grind up the crystals and mix it up with the water to get a paste. As for the taste, it would probably be sweet. Maybe like icing. Hmm, icing of Logic...The Sues wouldn't know what hit them. You could offer them a piece of cake with the icing then BAM! A pile of glitter.

I don't know if powdered crystal could be used to make icing...but we can improvise.

Think about it. Logic doesn't /seem/ appealing but tastes great and causes de-Sueification

Maybe that's what "concrit" does. It's not just a builoding material.

Glitter exists in its PPC form because Sues are often sparkly and speshul, and so, from a meta-standpoint, it was determined early on that Sueishness is determined by the presence of glitter. Glitter is almost like the smallest observable particle of Sue material. Admittedly, that's not the best comparison, but you wouldn't ask what the opposite of oxygen was, or the opposite of propane. Doubly so for semi-supernatural materials like glitter.
Fully supernatural substances usually have an opposite, but I'm pretty sure that's usually just to provide a phlebotinum antidote in case the creators write themselves into a corner, or in order to have a "dark" version of the existing substances to be used by an antagonist.

And don't let Agent Corolla hear you say that glitter tastes nasty. She loves the stuff.

Considering that a good chunk of Sues are written "on sugar highs" and often they contain too many "sweet" traits, we can assume that the taste of Sueness is a sugary one.

So the taste of Anti-Glitter should be bitter, but still pleasant. Coffee, perhaps?

Now that I think about it, coffee doesn't have that great of an appearance (it's usually brown), and tends to get one's head in place (for example, I tend to drink it oonly when I need help saying awake, as I'm not quite a fan of it. And it must be an Italian-style espresso, not that dirty water thing Americans call coffee)... so it kinda fits in all three categories.

As a result, we can safely assume that the closest thing to anti-Glitter existing is coffee.

…I submit three suggestions.

1. Chocolate

2. Guacamole

3. Pesto

Can't vouch fo de-Sueification, though. I'm leaning towards guacamole because chocolate is sweet and pesto needs to be cooked with other things. I'm seeing this as a "Oh no, she accidentally ate some of that Sue Soufflé quick grab the ________ and shove it down her throat!" situation.