Sugar Cube was a new neighbor of Orange and the gang's that moved in next door to them in THE OBNOXIOUS KUMQUAT. After Orange and the gang went in to meet their new neighbors, They had noticed that Marshmallow has a unicorn-shaped piñata, and Sugar Cube told him that They adored unicorns and that their father was a unicorn. They had very similar traits, as Grapefruit asked Sugar Cube what their gender was, and they quickly changed the subject. Their famous line is "Woo Hoo!" as opposed to "Yay!", which is Marshmallow's famous line.
Just like Marshmallow, the sugar cube's gender is unknown. When Grapefruit tried to ask, Sugar Cube just said, "Let's change the subject!"