S.H.I.T.
Manure - In the 16th and 17th centuries, everything had to be transported
by ship and it was also before commercial fertilizer's invention, so large
shipments of manure were common.
It was shipped dry, because in dry form it weighed a lot less than when
wet but once water (at sea) hit it, it not only became heavier, but the
process of fermentation began again, of which a by-product is methane gas.
As the stuff was stored below decks in bundles you can see what could (and
did) happen. Methane began to build up below decks and the first time
someone came below at night with a lantern, BOOOOM!
Several ships were destroyed in this manner before it was determined just
what was happening. After that, the bundles of manure were always stamped
with the term "Ship High In Transit" on them which meant for the sailors
to stow it high enough off the lower decks so that any water that came
into the hold would not touch this volatile cargo and start the
production of methane.
Thus evolved the term "S.H.I.T," (Ship High In Transport) which has
come down through the centuries and is in use to this very day.
You probably did not know the true history of this word.