Here's the way I heard it, delivered very deadpan, many years ago, when the subject of school plays came up in conversation:

"I was in a play once, but I got all messed up."

(Pause).

"I only had one line, but I messed it all up."

(Pause)

"My line was: 'Hark, fair maiden! I come to snatch a kiss, and fill your soul with hope'—but I messed it all up."

(Pause, while shaking head sadly.)

Then the laughter started. No further words were necessary—a prime example of how some things are best left to the imagination.