Let's say you have a close friend that has a problem with lows. For one, they tend to get combative when low and will start arguments or say really mean things (I mean, the things they think but shouldn't say type of things, not things they don't actually think). They get angry if you try to get them to test, and refuse to test again after treating. They don't like to carry supplies with them, and will often leave the house without even taking a meter, and usually don't have anything along to treat a low with. (Despite this, their control is not that bad, if you don't know about what happens during lows.)
Now let's say this also happens while the person is driving. Needless to say, testing before driving is right out. They get angry if you realise they are low and try to get them to pull over. Or if you, as I did recently, refuse to get back in the car until they test and treat, then get angrier when you insist they test again before leaving (still low). I know the anger has a lot to do with the being low, but there is obviously a serious issue in there. I guess I feel like even if they don't, I have to take my own safety seriously. (I have given up on trying to be concerned about them because it's not welcome). In the past, I have refused to go anywhere with them driving, but eventually I was unable to stick to it, because I don't drive. Plus occasionally there will be periods where they start acting more responsible.
No amount of cajoling or lecturing will make this person listen to me. Any hint of concern just annoys them. I finally just resigned myself to always carrying five times as much sugar as I would need, and always having lancets so I can switch them out and they can use my meter. That is, if I can talk them into it. I think there are two things going on here - 1. the belief that there's no need to be prepared, because nothing "wrong" is going to happen, despite all the evidence to the contrary, and 2. the idea that they're not impaired while driving with low bg, which I can say is untrue.
So...what would you do? Assuming you are still going to be friends.