When using a Riptide trident in rain, randomly, the player will be damaged as if they hit a wall after riptiding. Since you can riptide indefinitely through the air in rain, you can reach incredible speeds even without an Elytra. Because of this, randomly receiving damage midair has proven to be lethal, which is frustrating because you die mid-air very suddenly and lose all your stuff in an inconvenient location. I have a theory that when you riptide into an unloaded chunk, then that chunk loads in, the game thinks you collided with something, and gives you damage according to your speed. This also happens in fully-loaded chunks though. I can jump, riptide horizontally, then hit the ground less than half a second later, and it will deal a lot more damage than I feel it should. I always wear maxed diamond armor when I riptide for this exact reason and it still has the capacity to be lethal.

To recreate my experiences.....
-No resource or behavior packs, just vanilla Minecraft.
-Rain (though sometimes I will be damaged in the ocean or a body of water)

Items
-----Trident with Riptide III
-----Full diamond armor with Protection IV, and boots with Feather Falling IV (along with all the other enchantments, but those are the ones that would matter)
*All of this has happened without ever using an Elytra or fireworks.
-----No status effects, but the results are identical with Conduit Power III
-There is no way I was able to consistently reproduce results; I am speaking on (seemingly) random occurrences
-Results vary entirely from half a heart to instant death