What the hell is サンクソ? It's not in my electronic dictionary, nor in Nihongoresources or Wikipedia, and a Google search only demonstrates that it's widely used.

It is サンクリ(sankuri), not サンクソ(sankuso).
サンクリ is an abbreviated designation of "Sunshine Creation".
http://www.creation.gr.jp/

comment #38800
It's good to know that. Welcome to Japanese, the language where you can mistake one single letter and end up with a valid word.

三くそ！