I think every flipper has done this at leat once. (Whether they'll admit it is another thing.
)
Generally when I am setting up a bike I'll loose-assemble the handlebar clinch-bolt.
You can probably guess the rest but it gives especial meaning to the term "drop bars".
Thankfully, I do a hard shake-down on any bike I put up for sale and thus my buyers have been spared from my boo-boos.