Ping-pong was a familiar pastime at MIT. We also created some interesting games that involved five or six of us running around a ping-pong table while hitting the ball to each other. We also developed a game called "fling-flong". Let's just say we were creative with our table tennis variations.
The ping-pong ball of choice for most of us was Halex. If there could be a premium ping-pong ball, Halex made it. Halex balls were favored because they were evenly-balanced, not lopsided. You knew that by the sound...and by the way they bounced. A well-made, evenly-balanced ball goes "tink" on the table. One of those cheap Chinese balls goes "clink" and doesn't bounce in a straight line. In fact, you can't really tell the difference between a cheap ball and one that is damaged.
It was easy to damage a ping-pong ball. If you stepped on it, it would either crack or it would crease, which is almost as bad. Once a ball gets creased, it is hard to get the dimple out. Not that there aren't those who will try. The thing to remember about ping-pong balls is that they are thin, delicate membranes enclosing a volume of air. Air, when heated, expands. And that membrane is stretchable. So you can heat a ping-pong ball in a way that will cause the crease to come out of the skin, but you can't heat it too much...
A ball in this condition is said to have elephantiasis and cannot be salvaged. The only sensible solution is to sacrifice it to the Squirrel Gods. Which we had plenty of occasions to do.