What a great story. I am sitting here, reading this, chuckling because I could feel your pain, frustration and urgency. I know how you feel up until the final moment because this has happened to me a few times, I am rushing to get home or a nearby service station, but I normally just say to hell with it, pull over, find a bush or bunch of trees and let it rip. I have even used leaves/grass to wipe myself....
I have done the "I got a nice fart coming....shit, damn, darn it." but not the full turtle head coming out.
You are a very good story teller.
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Life's jounney is not to arrive at the grave safely in a well-preserved body, but rather to skid in sideways, totally worn-out shouting, "Holy sh*t! What a ride!" - unknown