Some characters in BFDI have "WTH" (what the heck) moments, where the character exclaims "What the" and then something related to what object the character is. For example, Snowball says, "What the flake".
In "How Loe Can You Grow?", Gelatin says "What the meat" in response to Four asking the contestants to improve the sun, confused how to do so. In real life, gelatin is made out of leftover boiled animal skin, bones, and horns. Not only that, but Gelatin also runs a restaurant called Gelatin's Steakhouse, which he might be referring to as well.
In "Barriers and Pitfalls", Golf Ball says “What in the spherical world was that for?!” when Tennis Ball kicks Rocky over the pole. Even though this is not a WTH, it counts as one, because "What in the world" and "What the heck" are similar.
In "Thanks for 4 years of Thanks for 4 years!", Match says "What the woodsicle" which is strange since "woodsicle" is a reference to her "God" (see Character OMGs for more information). This line was used once.
In "Fortunate Ben", Pen says "What the flip" in response to Liy revealing herself. This line was used once. There is a real life object called a "flip pen" that is used for pen flipping tricks, which is likely what Pen was referring to here. It's also possible that he was referring to Liy's flipping of her own switch and face.
In "Welcome Back", Pin says "What the corkboard" while asking Fries what he was doing. This line was used once. This line was used since Pin is a push pin, and push pins are placed on a corkboard to hold papers.
In "Getting Teardrop to Talk", Taco says "What the stand" in response to their team being one of two that haven't finished. This line was used twice. She could have said this since tacos, in real life, are sold at a stand, bought, and eaten.