I struggled for a while trying to think how to type it. Donk was my first one to go to but it didn't evoke that hollow part of the noise when it hits you
I absolutely love the nipple. I wish more keyboards had it. I have a decent mouse, however if I had a reasonably priced mechanical keyboard with a nipple it would be brilliant.
It reminds me of a game called "Völkerball" we have here in Germany. I suppose that is our equivalent to dodge ball, which I think this is in reference to.
I need to fresh up some memories here. Have you played it only after sports classes "just for fun" and have you played it with a so called "medicine ball" which made like this sound when hitting someone on the tighs or stomach: "PHHTHUMPBUMP" where the last BUMP is from the echo the impact made through the sports hall? All I know is I hated it the same as being a keeper in handball.