One thing you’ll know if that your nether regions are probably the most sensitive parts of your body. So you can be fairly sure that you don’t ever want a crab to grab hold of your balls while swimming.
The video is taken from somewhere in Thailand and doesn’t really have much of a back story other than that the guy seems to have got a crab attached to his nuts while swimming through a nearby river:
Damn. That looks like the worst thing ever and is quite high up on the list of things I hope never ever happen to me or anyone I know. Seems like crabs are NEVER a good thing when speaking in relation to humans.