Hardly ever been disappointed, but a very ill-matched concert was the Guess Who w/ Mothers of Invention headlining. Everyone had come to see Zappa, so didn't want to sit through GW brand of mainstream pop.
Fed up with the cries of "We want the Mothers!" and more pungent insults, Burton Cummings spat into the audience. Finally they walked off stage as it was inmossible to hear anything over the cat calls and booing.
Finally, the Mothers filed on stage, followed by Zappa, pulling a large gunny sack, from which he produced a variety of vegetables. These he examined with a stethascope, one by one -- rutabagas, potatoes, carrots.
The crowd started up again, booing, shouting for "Louie, Louie" (as only the Mothers could play it!) and other standards and throwing projectiles onto the stage.
Finally -- taking off the gas mask he'd donned -- Frank walks up to the microphone and says: "Kinda brings out the animal in ya, don't it?"
Actually, this was a memorable concert, so maybe I've never been to a really bad concert. Was there a best concert thread. Plenty of those to report -- not just one.