Choonis is the informal combination of two roots:
püooniʅ (poonis, havishamical origin)- which is an unnatural peenis that is capable of using suction and has various organic attachments, very few are born with these and they are assumed to be extinct.
chode - a fat penis with great girth and little length.
Hence choonis, which was used as an insult to those who were born with poonises. But since these people are extint it is currently used as a generic insult
Man that guy was such a choonis, he stole my grilled cheese sand-witch!!!!! (and I do mean a witch)