Back in the day when Oil cans were just that... "Cans" they used to bend and warp when you squezed them dry after pouring them into your engine.
The term implies that some boats will permanently warp under the cockpit from going over rocks etc... This leaves the boat looking less than sturdy, but never has it been proven (that I know of) to actually lead to anything much more than cosmetic issues. Some manufacturers are more guilty than others... All being the same, I still do my best to not purchase boats that oil can that bad.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body. But rather...To skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming... WOW !!!! What a ride!!!!!!"