"White cock," a phrase invented on lol_meme, describes juggernaut ships based around two white male characters when is was another, more-obvious ship to be had that includes a non-white character. The ur-example is Shawn/Lassiter (Psych): Gus canonically is super BFFs with Shawn, while Lassiter has a comedically antagonistic relationship with him. Frequently used in conjunction with Any Two Guys (who generally happen to be white) and Migratory Slash Fandom.
Over time, there has been a growing tendency for fans and memers to use the term to mean any ship made up of two white men, regardless of the context, usually to scold people for not writing more about women or PoC. This often causes disputes.