“I’m only speeding because I really have to poop” (bumper sticker)

“I’m only speeding because I really have to poop” is a popular jocular bumper sticker.  “I’m only speeding because I have to poop” has been cited in print since at least 2007.
 
“I’m speeding because I have to get there before I forget where I’m going” is another bumper sticker about speeding.
 
     
yelp—Talk San Francisco
What Bumper Sticker Should Be On Your Car? 
3/5/2007
B.K. W. says:
I actually saw one this past Saturday that said, “I’m only speeding because I have to poop.”
Yeah.  Real nice.
 
Twitter
Nikki Murray
‏@buttershug
Looking at a bumper sticker on the car in front of us that says: “I’m only speeding ‘cause I really have to poop.”
1:20 PM - 29 Apr 2007
   
Purple Slinky
Funny Bumper Stickers
Published by Dambrath in Travel
December 2nd, 2007
(...)
118. I’m only speeding because i have to poop.
 
Google Books
Where the Pavement Ends:
Retreats at Assumption Abbey and Other Contemplative Journeys
By J. T. Knoll
Bloomington, IN: iUnvierse
2009
Pg. 278:
Which is why, I imagine, the sticker I’M ONLY SPEEDING BECAUSE I HAVE TO POOP! caught my eye a few days later
 
Google Books
Travels with Max:
In Search of Steinbeck’s America Fifty Years Later
By Gregory Zeigler
Salt Lake City, UT: Blaine Creek Press
2010
Pg. 114:
Her car had a bumper sticker that read, “I’m only speeding because I have to poop.”
 
Google Books
When I Was Alive
By Rosalyn Hanson
Xlibris Corporation (Xlibris.com)
2010
Pg. 197:
“Honey, Nick has a bumper sticker on the back of his truck that says ‘I’m only speeding ‘cause I really have to poop.’”