Green’s Dictionary of Slang

the anus; thus chocolate starfish under chocolate adj.

2000		M. Manning Get Your Cock Out 78: Being shafted by a mongoloid whorebag pumping a strap-on Donkey Long Intruder up his starfish didn’t even bear thinking about. [Ibid.] 87: He was going to find out what a Gibson Explorer felt like jammed up his pink fucking starfish arse.
2012		(con. 1980s) I. Welsh Skagboys 500: Pin the starfish wi that auld shillelagh ay yours.
2015		‘Chelsea G. Summers’ in Vice 10 June 🌐 Balloon knot, bunghole, starfish, back door—we like to use metaphor when we talk about our assholes.