Intellectual blue balls
When you are engaged by an intellectually stimulating lecture/address/speech, or even just an enthralling conversation, and the speaker approaches addressing a topic of great importance to you, but then they abruptly change course and trend into new areas of discussion, leaving you with an overwhelming feeling of frustration and angst.
President Obama: one of the great challenges of our generation is to find an answer to the question about whether Han Solo or Greedo was the first to shoot...

Cletus: OMG, yes, yes, please, oh god, keep going, yes, yes, YES! ...

President Obama: that being said, we must engage in more constructive discourse about important clauses of the Trans-Pacific Partnership, particularly how it will help combat the illegal logging industry.

Cletus: wait, what? Intellectual blue balls...NOOOOOOOOOOOOOOOOOOOOOOOOOO