At the campaign level, go to "exclude sites" and enter in any URL you want - this site will be excluded.
A few caveats (big caveats):
1. This only works for content network, not search network;
2. You can't exclude the Google domain parks from this (anything that says apps.oingo.com). The reason Google gives for this is that domain parks are a hybrid of search and content, and since you can only exclude content-only sites, these pages don't qualify. So site exclusion is somewhat limited in this regard.