My college band and I got onstage at a charity bluegrass concert one night; we were never known for our polish but we didn't usually embarrass ourselves this badly. First, our ordinarily mild-tempered fiddler dropped his bow and blurted out, "Sh*t!" into the microphone--in front of an audience of retirees, no less. We got through "Big Scioty" just fine, but when we went on to "Hell on the Wabash", which sounds nothing like "Big Scioty" all six of us at once forgot the B part and kept slipping back into "Big Scioty". Finally, after two restarts, we gave up, apologized to the audience, and switched to A.
We rarely sang or I'm sure we would have come up with some doozy spoonerisms, too.