While balls deep in a vagina from behind whilst wearing a skeleton costume and a pink sock starts sneaking its way out, quietly peel off an arm bone and jam it in her anus while you continue merrily on your way to ejaculation.
Last Halloween, I had to Jack Skellington this nasty hoe before her pink sock exploded on me.
Popularized by Jack Skellington from Tim Burton's The Nightmare Before Christmas, but also used in place of skeleton as seen in Scarygoround, a webcomic by John Allison.