Experienced it this morning on the commute into work. Traffic wasn't too bad, but it backed up enough to ruin my ride and folks were parked in the left lane going really slow.
So since my exit was coming up soon, I finally moved over to the far right and the exit ramp is fairly long, probably about 1/4 mile long and clear. So what did I do to vent my frustration? Downshift to 4th and run it up to the shift light! I didn't dare look down at my speedo, but you can pretty much guess what my speeds were @ 14k rpms in 4th. Anyways, as I'm fully tucked in with the throttle pinned, the handlebars start moving and the bike wiggles a little. I instantly ease off the throttle and get straighten up off the tank to help scrub some speed without upsetting the bike.
Now I'm online looking for a stablizer.
Anyone experience a really bad tank slapper? It was in a heat of the moment kind of thing, but I don't think I'll be doing this again anytime soon. Most of the time I'm just cruising and enjoying the sun and open road.