Docking is a sexual act of putting the head of one's penis inside the forskin of another's, and is often referenced to by the NLSS crew.
Docking was first mentioned by Josh and Nick during the NLSS. The word came up and incited Nick to remark that it was an actual sex act. Upon describing said act, Ryan wondered jokingly how a man would propose to his partner to engage in such an act, and the idea was planted that perhaps they would text each other requesting "permission to dock". The word has been an inside joke of the show ever since.