A hokey is another name for a VERY VERY loose vagina. It is derived from doing the Hokey-Pokey where you "put your left leg in, and you shake it all about" ... etc. If you can put your leg in and shake it all about in a girls vagina, then it is a hokey.
Me: man this girl i got with last night had a major hokey
friend: oh yah what do you mean?
Me: i put my whole self in and i shook it all about.