Sorry but I laughed at this. Chicken keeping summed up in one sentence!
How secure did the nipples seem when you set up the waterer? (Wondering if you could've accidentally used a drill bit that was slightly too big, or different nipples than you'd used before which required a different sized bit, or if they might have not been screwed in quite far enough or have some kind of manufacturing fault that caused them to be loose and come out easily, or you used a different kind of container for the waterer that was made from a thinner material than you've used before.)
Are the other waterers you haven't had issues with set up exactly the same, with the nipple at the same angle and the waterer itself positioned the same way? Some chickens will do a fairly aggressive peck or bite and grab to drink from vertical nipples, so possibly the nipples being at an angle has made it easier for them to get unscrewed over time if one or more of your birds drinks like this. I'm not sure but possibly the waterer being placed in a way that meant the nipple was always grabbed from a particular could contribute to this.
I tend to put a tiny bit of silicone sealant around the very end of the threads at the point where they'll be in contact with the waterer when fitted. (Easiest to paint the silicone on with something like a toothpick before you start to screw the nipples into place.) It helps prevent leaks if the surface the nipple will sit against isn't totally flat or rigid, or edges of the the hole they're fitted in are slightly uneven, but it would probably work a bit like an adhesive too unless the chickens are really going at it.