I'd pulled a blooper, but how was I to know until too late?
"The Old Die Rich"
Horace Leonard Gold
The magician-in-public-practice needs only to make one really bad mistake before he is done to some unpleasantly ingenious death by his clientry, and this was going to turn out to be the biggest magico-prophetic blooper in all the long unrecorded history of Kwannon.
"Oomphel in the Sky"
Henry Beam Piper