Starfleet diapers
A diaper is a type of cloth garment, usually worn by infants, to aid in containing bodily waste.
During a conversation, where a 17-year-old Sim expressed his interest in T'Pol, he felt that her declining his invitation had something to do with the fact that he was "different," figuring, "I guess it must be weird, being with someone like me. Five days ago I was wearing diapers." (ENT: "Similitude")
In an argument between William and Kyle Riker about Will's mother, Kyle argued that Will was "barely out of diapers when she died!" and that he "hardly knew her." (TNG: "The Icarus Factor")
Following repeated offers by Montgomery Scott, in 2369, to assist Geordi La Forge in Engineering, which ultimately resulted in La Forge telling Scott that was "in the way," the angry Scotty retorted that he "was driving starships while [La Forge's] great-grandfather was still in diapers." (TNG: "Relics")
In a similar vein, during their encounter in the Nexus, James T. Kirk remarked to Jean-Luc Picard that he "was out saving the galaxy while [Picard's] grandfather was in diapers." after the latter reminded him of his duty as a Starfleet officer. (Star Trek Generations)
After deciding he wanted to mate with Kes in 2371, Neelix made his announcement to her by stating "order the diapers, we're about to become parents." (VOY: "Elogium")
In an alternate timeline, Linnis Paris acknowledged that to her mother that seemed to be "much more comfortable with a molecular scanner than...with a diaper." (VOY: "Before and After")
In late 2377, Harry Kim gave Tom Paris and B'Elanna Torres a diaper, with a Starfleet emblem embroidered on it, as a gift for their baby shower. Kim claimed that garment was "standard issue." (VOY: "Human Error") Later, while contemplating their future, following their return to Earth, Torres figured that Tom would probably take the first piloting assignment that comes along and leave her home to change the diapers. (VOY: "Endgame")
In an alternate 2378, Linnis Paris noted that she was far more comfortable with a molecular scanner than she was with a diaper. (VOY: "Before and After")