Earth needs a bit more than fabric sometimes. Not only can that water fall in the solid phase, occasionally it moves really fast!
A SCBA isn’t an umbrella. The rain is just more conductive atmosphere though, so you’d need a higher setting on your personal heater.
Neptune probably doesn’t have ground, and HD 189733b definitely doesn’t. Anything capable of surviving the pressure at that depth would probably be fine, although we don’t know how large the diamonds would be or how sharp the flakes that form are. Diamond Shuriken Rain sounds like an awesome song though.
OGLE-TR-56b also probably doesn’t have any ground, but depending on how high you’re flying you might want something non-stick. Tons of iron welding itself to you is possibly the worst case of wing-icing you can find in nature.
