@WeBuiltThisBuffetOnSausageRoll so can you hand on heart say that you would rather just say to a stranger “can I have a biscuit”. No explanation nothing than explain why?
Really? Honestly? Would you?
I would probably say "My energy levels/blood sugar are dropping or I feel a bit faint". I wouldn't use the word 'diabetes', because announcing it often leads to unwanted assumptions/unnecessary panic/judgment.
I agree with what you said about 'diabetes' but this is probably why I am get to meet someone with Type 1 diabetes (ie the more-likely-to-hypo type) who doesn't say they are a 'type 1' (and then possibly go into a long tedious explanation between the two, or maybe that's just me...)
A lot feel duty-bound to do so to stave off prejudice, but IF I ever do mention it, I personally would never mention which type - unless it naturally developed into a more detailed discussion.
I've heard other people with T1D say they would like it to be given a new different name to distinguish the two, so that they avoid being lumped in with the stereotyped 'fat, lazy, brought it on themselves lot'.
Of course, people are free to believe/want that and manage/cope with their own condition the best way for them; but personally, I hate the seeds of division that are sown, as if those with T2 are 'the baddies' and those with T1 are 'the goodies'. We all have a related serious medical condition and I don't see why it should treated like a competition.
It's not like, say, mentioning what happened when you were in prison and then quickly pointing out that you used to be a prison officer rather than a convicted criminal. I'm not generally a fan of disability/poor health-blaming.