Usually it just means somebody who supports the SDLP instead of Sinn Féin, but since the Good Friday Agreement the ultra diehards have started to regard Shinners as just another set of stoopers.
The term "stooper" is associated with the adjective "ganked" (see example). A "stooper" is significant, because when a post is located at the top of a page, it will be seen (by most users) every time the page is loaded.
Swood: I disagree, the Shins pretty much such my nuts. I hope they never come back to concert in Minneapolis.
Woogums: Ohhh Swood.. you just ganked the stooper..