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Butt garments is a CWC-ism for diapers, which are used to prevent DIRTY, CRAPPED BRIEFS (or fecal leakage, where one unintentionally shits themselves). He most likely calls them "butt garments" to avoid the embarrassment of wearing diapers, despite the fact that he desperately needs them. Chris hated the idea of wearing diapers, and made multiple attempts to throw out the diapers before Barb caught on and hid them away in her room.
On 16 April 2009, images of Chris in diapers leaked, with a special shout-out to spas from #sonichu. Chris later stated in ECV 00095 that the butt garments were sent to him by a troll. According to Ivy's ghost, Barbara mistook them for samples of adult diapers sent by Chris's doctor, who had been trying to convince Chris to start wearing them.
After Ivy found out that Chris was cheating on him with Vanessa Hudgens, one of her friends suggested that he take the photos below to apologize to Ivy. The front reads "TOO HOT FOR COLLECTION," in case you don't want to stare at it for too long. This appears to have been the last time they were ever mentioned. Presumably, they are still sitting around Barbara's bedroom.