I heard of a incident where brakes were applied accidentally(although almost wet myself when I was told) ...
A colleague of mine, a CC member on a B737-3, decides that it is easier to balance at the overwings, during safety demo on taxy, by lodging his feet under the metal bag restraints under the aisle seats.
During a fairly fast taxy out, suddenly the brakes were slammed on, sending him leaning back fast. Grabbing the seats either side of him to stop him falling backwards onto the aisle floor, the seatbacks folded forwards forcing two pax into the brace position!! Ouch.
Wouldnt have been as funny if it hadnt have been for the fact the demo had just reached the part "if you hear the words brace, brace, you must take up this position immediately".
Mal mate, where are you now???!!!