But why is # 'bash' rather than 'hash'? I'd be inclined to call either # or % 'hash'.

You nearly answered your own question. 'hash' seemed a bit ambiguous.

It wouldn't occur to me to call % "hash". It looks more like a sneer to me so sneer is what I call it

Never got my head round ! as "bang"; it's always been "shriek" to me. I wonder if this is a transatlantic difference or a generational one? Maybe us rightpondians are less familiar with things that go bang than our leftpondian cousins (but let's not go there; it usually ends in tears). What became of "pling" anyway?

^ is always "yay" to me as it feels like throwing one's hat in the air.

Readers not familiar with Glasgow sporting (and other corresponding) loyalties probably won't appreciate \ as "Rangers slash", / as "Celtic slash" and | as "Thistle slash¨.