I've been to literally, thousands of concerts over my life, including some of the bands mentioned on this thread, can't recall a single incident of a really bad concert. Some didn't live up to my expectations, but not what I'd call bad.
Since we're picking on Bob, did see him at some outdoor venue many years ago, real Dylan fanboys out there, thought the concert mediocre at best, seemed like disinterested and distant person/performer to me. Thing I most recall most is how the fanboys just loved this mediocre concert, certainly cult of personality thing going on there.