This didn't happen to me, but my buddy and I were out one day and stopped at a book store to kill some time. As we entered the building, he made a bee line for the bathroom and told me he'd find me in a few minutes.
About 10 minutes later, a bit red faced, he told that he entered the bathroom and saw that the first stall was occupied. The second, and last stall was open so he ducked in. He had his Beretta Tomcat in an open top holster and was careful to make sure the gun was secure as he dropped pants. After taking care of business, he stood up, and in slow motion, he saw the holster twist and the gun slid free. He was certain that the gun was going right into the john but as luck would have it, it didn't. It did however hit the ceramic tile floor and slide right under the wall separating the two stalls.
My buddy said he stood there a second, dumbfounded, then quickly reached down and retrieved the gun. He finished dressing, washed his hands and beat feet out of there.
The best part was that he said he never heard any thing louder than the sound of that gun hitting the floor and then sliding across the tile. He also said he never heard any thing so quite as the stall next to him once that gun slid under the wall.
My buddy of course had his CCW license but we thought it best kill time some place else after that.
"He who laughs last, laughs dead." Homer Simpson