Cockles is a "pairing mashup" - a portmanteau of (Misha) Collins and (Jensen) Ackles - used to indicate those characters are Slashed in a fanfiction or other fanwork. It tends to be used in crack rather than serious sense. Except by Tin Hats who actually Jensen adn Misha are in a relationship. However as a Slash mashup name it is rather awesome as it contains the word "cock".
In November 2013, Misha posted a link "accidentally" to a tumblr post titled "The epic love story of Jensen Ackles and Misha Collins.