In the 16th century, most everything was transported by ship and it was also before the invention of commercial fertilizer, so largeshipments of manure were common.
It was shipped dry, because it weighedless but once water hit it, fermentation began which produced methane gasas a by-product.
The manure was stored in bundles below deck and once wet with sea water, methane began to build up.
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 had happened.
Afterwards, the bundles of manure were stamped with the term "Ship High In Transit" which directed the crew to stow it in the upper decks so that any water that came into the hold would not reach this volatile cargo and produce the explosive gas.
Thus evolved the term "S.H.I.T " (Ship High In Transit) which has come down through the centuries and is still in use today.
You probably did not know the true history of this word.
Neither did I.
I always thought it was a golf term