I’ve never heard of it before, either.
UrbanDictionary gives this definition:
Quote:
Someone who can consistently, without fail, through precise and accurate employment of donkey-like tenacity and interminable aimless wanderings of thought and conversation, completely annoy the holy living dog-fuck out of a poor unsuspecting victim.
Sometimes causes one's brain to simply shut down, leaving the victim stunned, lifeless and turgid.
I don’t quite see the relation to cooking here, though … :P
Edit: This site gives a more relevant definition:
Quote:
Bastable: the three-legged iron cook pot still very much in use in Irish country kitchens. It is hung on a hook above the peat fire in the open hearth and is used for soups, stews, potatoes, and even baking. The famed Irish soda bread is made in a covered bastable.

I’ve no idea what that would be in Irish …
I would guess that (for whatever reason) this pot is named after the family name Bastable. There might not be an Irish word for it at all.