From my short bit of trying, and of Google searching, it seems like there is no way in vBulletin to search for an exact phrase.
However, you can use Google to search for the phrase. It won't search the Cursing Out Coworkers or Morons in Management forums, since they're not public, but you can go to Google, and enter this for your search:
site:customerssuck.com "sucky manager"
And that will do the search you're looking for.