To come up with a complete non-sequitor in a conversation. The entymology of this word began on The Geek Show Podcast when panelist Leigh George Kade would be accused of completely derailing conversations with completely irrelevant information. One day, when he wasn't there, a fellow panelist decided to "fill in" for him and shouted "Blueberries!" for no reason.
It's caught on with the audience of the show and is a recurring declaration when an irrelevant, derailing comment is made.