I'm going to be a Grandma, and have been asked to come up with a Granny Name.
I am not a reputable grandparent. I do ... all the things. And the grandpa is even worse than me. So I guess suggestions for either of us are welcome ... I'll pass them along.
So far, frontrunners are Supreme Leader, Duchess/Your Grace/Your Disgrace, Dowager Mother, and Mimsy "short for Borogrove".
I don't have any kind of interesting ethnic background for inspiration, except that I'm originally from America and grew up in the UK. I've always liked "Grandma" (what my American relatives used).
We live in Wales, but I'm not Welsh so I think "Mamgu" would be inappropriate.
I'm not really expecting serious suggestions, I'm quite happy to default to whatever they call me, just having a bit of fun because they did ask. As you can see the suggestions my friends have made so far have been quite off the wall.
Now I need to order some Werther's Originals ...
Edit: thank you everyone, I read every comment and enjoyed all of them even if I didn't reply. Mimsy (Short for Borogrove) is looking like a clear winner, but several other great suggestions. Particularly fond of Gorgon and Supreme Allied Commander. Oh and Original Product Manufacturer (OPM). I had a great laugh reading this thread! And it was lovely hearing all the sweet ones too!