The fetish box is a hypothetical container which everyone posesses. In this box is stored any item which, by the assossiated definition, is regarded as a fetish.
The fetish box is typically closed at any given time, though few rare circumstances can result in other people becoming aware of the (sometimes many) fetishes held within, this is "opening the fetish box".
The fetish box can also be used as a short term storage device for any comment, conversation or action which needs not be had at the time it is considered, in this case, the conversation, comment or action is "put in the fetish box"
"I cant do this right now, put it back in your fetish box"
"I cant believe you just went and opened your fetish box, what the hell were you thinking? I didn't want to know that man, far too much information"
"That's some kind of chronic weirdness man, dont tell anyone that ever again, put it in your fetish box"
An imaginary storage device which everyone possesses in which is kept filthy, perverse desires.
Dude, I don't want to know, put it in your fetish box!