Does J. ever accidentally sing the original lyrics to a song onstage?
Thankfully, that hasn't really been a problem.
The only real problems I've had was doing a song we've spoofed twice. Our original parody of "Every Crown Has Its Thorns" (on the "Want It Dead or Alive?" tape) was called "Every Road Has Its Cross." I slipped up once and started singing that chorus, "Every Ro ---" and I think the people thought I was singing "Every Rose Has Its Thorn" like the secular original, but I wasn't.
Even more troublesome is the original parody we did of "Stairway to Heaven," called "Yourway to Heaven." Both that and "Narrow Way to Heaven" are about the same topic, but they have very different words. Unfortunately, I still have to watch myself to make sure I don't start singing the old parody lyrics, because they never meet up with the new parody lyrics. You'd think I'd be used to the new version, seeing as we've been playing it since 1998, but we did the first one from 1992-98, so it had plenty of time to be embedded in my mind.