Well, so many wonderfully silly things have been mentioned here already that I hesitate, but - for the record -
How about the "Creative Days were exactly 7,000 years each"?
Now, just exactly how did that ever see the light of day? - The Bible could possibly have said (just as a matter of expression) - that "a day with God is like a thousand years". Now, of course - an Earth day is the usual approximate 24 hours, a Lunar month is the usual Lunar Month, and so on. Simple Geological evidence will show the Earth to be literally MILLIONS of years old - but no matter. The creative days were seven thousand years...no more, no less.
But may we just ask: where - where? where? can you find anyplace that the creative days were seven thousand years long? (Other than the Freddy Franz version of the Watchtower?)
If you were not a student or observer of this religion you might well ask - what difference does this quaint little teaching make? Well, if you had lived through the 1975 fiasco, you would know that the whole rationale of the 1975 end of days was that this was to be the end of the 6000 years since Adam. This left exactly 1,000 years in the last (seventh) creative 7000 year day, and conveniently, this would work out just right for the thousand year reign of Christ.
Or, maybe not. It was the Edsel of the Zion's Watchtower Society, and they are still in denial over it.