Some dwarf throws a potion at you while the umbrella is wielded in your
off-hand then the umbrella will take the brunt! Downside is no more cheap
identification of potions.

If it's a potion of acid then there's a chance the umbrella will be
destroyed.

Umbrellas would also be awesome tools while exploring dungeons as a way to
protect one's rustables which haven't been fooproofed yet.

Should the player forget to x the weapon out, leaving the umbrella as the
primary weapon, and the character is female then it would simply scare off
the beaten monster rather than cause damage.

Male characters would do minimal damage making it perfect for making Vlad a
challenge!