:smack: Grammy.
That’s hysterical.
It kind of reminds me of the family story (although this wasn’t a screwup) of how my grandmother’s brothers dared her to play “The Worms Crawl in, The Worms Crawl Out” in church. So she really jazzed it up and stuck it in during the offering, I think. Once her dad realized why his sons were besides themselves, he was mad. This was in about 1934, you have to realize.
My old trombone teacher told me that the difference between an amateur musician and a professional is that a professional can make you forget you heard a mistake 
Dolly Parton and Kenny Rogers we’re performing their “Islands in the Stream” duet live on some television show. When Kenny was to come in singing harmony at one point, he was way off key. He stopped after a few notes, laughed and shook his head in embarrassment, and waited a few bars before jumping in on the right note.
All the time. Was personally at a concert where the Oboist over blew during a solo. Unfortunately for her, there’s no disguising a mistake on Oboe.
Also just a couple of months ago I went and saw a performance of Beethoven’s 4th Piano Concerto. While I didn’t realize it at the time, my sister (who preformed in the orchestra) told me that the pianist actually missed an entrance. I pretty sure nobody but the orchestra and piano professors in the audience even noticed.
Here’s a YouTube vid of Yundi Li playing Liszt’s La Campanella. Listen VERY CLOSELY at 4:16. 
Then again this is one of the hardest pieces known to man, so I’ll give him a break.
That’s like what, one note a half step off out of tens of thousands? I’m still not even sure I heard it. That piece is like speed metal on a piano, it’s totally nuts.
David Gilmour forgot a good chunk of the second verse to One Slip during the Toronto, Ontario leg of the Pink Floyd Momentary Lapse of Reason tour in 1987. (The night Benji Hayward got high, left the concert, and drowned himself in Lake Ontario, for any who remember that incident) He didn’t even try to cover, he just kinda trailed off for a couple of bars and picked it back up at the chorus.
During her legendary Carnegie Hall concert, Judy Garland went up on a line of You Go To My Head. “You go to my head, with and I forgot the goldarn words.” I picked up another CD of hers which also had the song on it and was a little excited that I’d finally hear the song with all the lyrics. She went up on the exact same line again.
One of my favorite moments on a live recording is a non-flub that occurs in Stevie Wonder’s “Fingertips Part 2” when during one of the harmonica breaks you can hear bass player Larry Moses furiously asking “What key, what key?” The piano player responds by hitting a little 3 note run a few times. Its about 2:20 into the song, after the MC says “Let’s hear it for Little Stevie Wonder.”
Apparently, this was recorded at a Motown revue show, and everyone thought Stevie was done and the band for the next act - Mary Wells - was coming on stage. But Stevie had other ideas and came back out for a little encore. And so Mary Wells’ band picked up the last little vamp. If true, than super props to those new musicians who picked up a new song mid-stream in front of a live audience with tape rolling - and proceeded to blow the roof off the theater one more time.
Not a screw up by a musician, but a pretty major screwup by people you’d think would know better:
I saw Der Ring des Nibelungen at the Met in New York in 2000. At the end of act II of Die Walküre, the curtain came down about a minute and a half early–before Wotan’s dramatic vocal exit. It came back up again just in time to see James Morris storming off stage.
I would not have wanted to be that stagehand.
I remember this time I went to see a band called the Grateful Dead, and it seemed as tho they forgot how to end all of their songs - they’d just go on and on interminably! 
Regarding not showing when you made a mistake, my daughter is far from a pro, but is a pretty decent pianist, and plays in public quite often. When she started to play more difficult pieces, we specifically addressed the way she would react when she slipped up. She would know it, and we would know it from hearing her practice the same darned piece a trillion times, but 99% of the audience would have no clue. That is, they wouldn’t have had a clue if she hadn’t frowned, blushed, and looked disgusted.
It is amazing how badly you can mangle a piece and not have people notice if they are not very familiar with the piece or following with a score.
One time when she was younger, I was accompanying her on piano as she played flute. When I mangled the first few bars, I stopped the piece and said, “Let me try that again. I can do better than that.” And proceeded to hack it up even worse than the time before! Man, you should have seen her staring daggers at me! For some strange reason, she never asked me to accompany her again…
Jerry Garcia often blew a line in a song at least once every concert. Either he would come in at the wrong time or, would skip a verse or sing a verse twice. The Dead would just keep on playing, the crowd would cheer, Jerry would smile a bit and the show went on. It really became quite endearing.
Here’s a page of trumpet bloopers. Some bad, some really not so bad. Not all from public performances, but many are.
When I was in high school, our organist / choirmaster was really excited about leaving for his vacation on Sunday afternoon. He was headed to California to visit his kids I believe. During his modulation into the Doxology, you could distinctly make out “Cal-i-forn-ia, Here I Come”.
Mr. Renneckar, you were quite a guy & you are sorely missed.
[QUOTE=GorillaMan]
And even the greats aren’t automatons, technical perfection is not the measure of great music.
A ‘name the pianist’ game was played on me by a friend, with an LP of a live recording which AFAWK has never been rereleased. It’s the last movement of a Beethoven sonata, and it’s a tumultuous, haphazard and almost chaotic performance. Just about every single bar has spectacular mistakes in it. It’s hilarious, laugh-out-loud funny, but at the end the audience go wild. Go back and listen again, stop yourself from laughing, and you can hear that it’s also a spectacular musical performance.
No, I didn’t guess the pianist, but it didn’t surprise me that it was Richter…/QUOTE]
Richter hit a few wrong notes in “Pictures at an Exhibition” recorded in Sofia, Bulgaria, back in 1958.
Yet that recording–made with a crummy machine while the audience apparently coughed its way through a flu epidemic–is supreme artistry.
While in college, I took three years of German. We were required to pass exams in either French or German, but classes weren’t provided. One of my classmates, María, was a soprano; she had decided to start studying foreign languages because she was tired of having to ask for translations of the songs.
She was part of a 4-singers Mozart recital and I went with a friend. After the performance, we went backstage to say hi. Being from the other end of the country, María didn’t have anybody there; two other people had a small group. The fourth one, the tenor, had a very large group, all of whom were conmiserating him on having started one verse of a song one note off and having had to sing the whole stanza off-key. They were making such a fuss that we asked María “ok, I probably should know this, but… is it really such a terrible thing?” She shuffled things about, so she could turn her back to the large group discreetely and said “not if you ask me since he recovered but what can I say, not all primadonnas are women.”
Mozart sounds just fine one note too low, in my musically-not-very-educated opinion. I’m sure he’d disagree.
Possibly a neurological incident.
Sir Georg Solti, the legendary conductor, once stabbed himself in the forehead with his baton during a particularly vigorous movement. I think this is considered in musical circles to be at least a minor faux pas.
Yes: never stick your baton in the pencil sharpener. It’s all fun and games until, &c.
Bob Weir has also become… I dunno, famous? Beloved? For blowing lyrics in songs he’s been singing for 40 years.