The Glasses of Ultimate Smartness are a Woo Foo artifact that allow the wearer, no matter how stupid, to have unlimited intelligence, but since it has no effect on common sense, they also cause everyone else to feel miserable.
Too Much Yangformation
Because Yin tends to brag every time she "smoked" him in tests, quizzes, and other things marked on their Woo Foo report cards, Yang had a plan to beat her in their next history quiz: first, he continues "screwing around" (as his own sister puts it) in ways that distract Yin's attempts to study, and then he puts on the Glasses of Ultimate Smartness so he won't have to study... Yin points out that it's cheating, but does nothing to stop him. By the time the quiz starts (in the form of a Game Show), Yang is so smart that he could answer most (if not all) of the questions before Bird, in place of Yo, could finish asking them, giving Yin a taste of her own medicine and convincing Yang that he should never take the glasses off... ever.
Since Yang decided to wear the glasses all the time, his smarts are causing problems for everyone else, like figuring out the ending of a movie just by seeing the first few scenes, and ruining the surprises at Dave's birthday party by correctly guessing the gifts via package shapes.
Thoughout it all, Yang's natural lack of commons sense, combined with the glasses' ability to boost his brain-power and (unwittingly) his already large ego, kept him from recognizing Carl the Evil Cockroach Wizard while the villain was disguised as both a theater usher and a "poor confused foreigner" in order to trick Yang into giving him the recipe for the potion of huge-itude. Yin suspected something was wrong, but Yang, enjoying himself being smart way too much, laughed at her and said: "For a moron, you are adorable" causing her to cry (even though she kept telling herself that Woo Foo knights don't do that) and leave Yang alone wondering if he did that, making him vulnerable to a giant Carl!
Realizing later on that it's the brain-power boost that's making Yang a "big jerk-y know-it-all", Yin insists he takes them off, which he refused to do until she used the Transfoomation spell to change their original black, square-frames into pink and stylish "girl glasses". Grossed out, Yang not only removes the glasses, but also slices them in half, freeing himself in time to stop Carl's plans to blot out the planet's four suns, though he needed Yin's help to shrink the cockroach back to normal because she studied and he didn't.
In the end, the feminized Glasses of Ultimate Smartness are taped back together and given to Carl's mother, who used her new intelligence to make her un-favorite offspring cry using a lecture on how poorly thought-through his plan to blot out the sun really was.
- The Glasses of Ultimate Smartness don't appear in any other episode but may (or may not) be a topic in the works of fan-fiction.
- This object is based on the trope/belief that smart people always wear glasses, especially dorky square-framed ones.
- Yang found this artifact in a box of "Enchanted Flakes" cereal, which has the image of the glasses on the box advertizing it as a prize, which may hint there are several fake versions of it in that brand of cereal and Yang just got lucky in finding the real-deal.
- The fact this artifact is found in a ceral box might be a shoutout to a later episode, in which another Woo Foo object, the "Knuckles of the Infinate Smackdown" are hidden in a brisket (seems ancient warriors have a habit of thinking their enemies won't find important things in food).
- Master Yo knew all along Yang was using the glasses to cheat, but let it happen on account of Yin's constant gloating ("It's only fair")