1. Avian fecal matter. In the 18th and 19th centuries, the North American Guano Company would send ships to south-Pacific islands to harvest the guan, which was used as fertilizer. (seriously!)
2. Bad news or something unpleasant and unflattering.
1. We used to have to import our <i>guano</i> from Mocronesia, but today we produce so much bullshit in Washington, that we no longer need the bird shit!
2. Wendy really dumped a load of <i>guano</i> on me when she said we were breaking up!