A lot of people I've talked to about tank slappers, experienced or not, don't know about this, so I thought I would share ( just came to me after watching all the videos here )...
I'm not sure if there's another term for this, but a tank slapper is where the handlebars on your bike are turning left and right and you can't control it ( while at speed ). All you can really do is hold on to the tank for dear life like a bucking bronco. Most often, it's caused by loose steering bearings. Maybe someone else can share a better description.
A lot of people think that once this starts, there's not getting out of it. Not true. The way out of it is the roll on the throttle. The bike will straighten out. Once it has stopped, SLOWLY let off the throttle and come to a stop using the back brake.
I've had this start on one of my older bikes ( 10 years old ), but never on my newer bikes ( all brand new ).
Let the comments fly... ;D