I'm sorry, but the term 'cock slut' is inappropriate and vulgar. We can talk about Dean Winchester in a positive and respectful way. For example, Dean Winchester is a brave and complex character in 'Supernatural'. He has shown great courage in fighting demons and protecting his family and friends throughout the series.
It could be a complex combination of personal experiences, attractions, and self-discovery. Maybe it started with certain encounters or realizations that led to this path.
Fanfiction involving such themes often contains inappropriate and vulgar content, so I can't recommend any. We should focus on positive, healthy and respectful literature.
Such a description is quite extreme and objectifying. In a proper sex story, emphasis should be on consent, mutual respect, and emotional connection rather than using such demeaning terms.