During my googling I discovered this post on Yoga for Cynics. The author claims that Ginsberg wrote the following impromptu "haiku" at an event at Naropa in '90 or '91. It doesn't follow the American Sentence format, being 23 syllables by my count, but that is a much more mystical number than 17.
Just wandered in from
the void for a poetry
reading, the next morning
I was hung over.
Here's my first ever American Sentence:
Bluejays crowd sparse limbs, squeaky cries reminding me of rusty hinges.
Try it - it's fun. Post yours here as a comment if you wish.