Well, I have to jump in here.....one of the worst screwups onstage, by me, was back when I was in my first band, The Howling Gael. We used to open....every gig....with Steeleye Span's "Misty, Moisty Morning".....I could sing that song drunk or sober and in my sleep! But then I used to have nightmares about blowing the line ..."I'll plow and mow and reap and sow and she will sit and spin...". Never did, tho.....till we did a school gig and there I was in front of the entire 7th grade of the Mt. Tabor Middle School....and out of my mouth came the words..."and she will shit and spin..."! And yes, every single kid in that audience caught it!
My wonderful band partner in Broadside, Andrea Aldridge, wrote a great spoof (of the Shanty The Alabama), "When the Alabama's Crew Got Laid", which is, of course, the first line. So there we are, a bunch of us,(not Andrea)doing a big festival on the waterfront in Portland and one of the women tells the story of The Alabama, prior to singing the song...and sure enough, the first line out of her mouth is...you guessed! Stopped the two policemen passing in front of the stage dead in their tracks!
Hey, I like this thread!