Well, apparently one of them had been practicing a particular "trick." (S)he went up on stage and began a strip tease. Until the g-string came off, you would actually have been hard pressed to tell she wasn't a woman. Then, a nice floppy 10 incher made it out on stage. (S)he proceeded to grab the head and stretch the thing out repeatedly (imagine working a piece of salt water taffy). Then (s)he turned around and grabbed the head from behind and pulled it between the legs, up the crack, and placed the head firmly on the small of her back. At this point, the cock was stretched very thin and had gained at least another 12-14 inches in length to reach where it had.

Plus, I've seen a video online somewhere (can't find it right now) where a tribal looking dude take his cock, stretches it out multiple times (like the taffy again) and then rolls it up onto a stick (imagine bubble-tape). He then stretched it back out to double its original length, put it through a loop of rope attached to a pretty big rock, and lifted it and swung it around.

So yeah, I'd reckon that the cock smashing feat we have seen here is possible.

edit - Found the video of the dude stretching out his cock and lifting a rock!

edit2 - apparently "video of a dude stretching out his cock" after the long explanation above it was not enough for some people to realize the video is NSFW. So, yeah, it is NSFW. (pro-tip: if it has the word "cock" in the description, probably NSFW)

edit3 - I've been disabused of the notion that someone couldn't tell it was NSFW. I apologize for taking it seriously. I spend a fair bit of my time debating creationists and alternative medicine shysters, and the shit coming out of their mouths makes such a statement seem quite reasonable. Guess I was in that headspace. :-)