You can throw a riptide trident if you're not completely in water

The bug

You can throw a riptide trident if you're in water only with your feet.

How to reproduce

1. Make sure it isn't raining

2. Get a riptide trident

3. Place water (one block deep) and enter it

4. Notice that you're able to use the trident

This also works with waterlogged blocks (for example, slabs).