I can already imagine...
"Oh, I'm already out of money and unemployed but I need to have an emergency surgery done. Would you really be so cruel to not help me? It's just money, I will pay you back, I swear! Don't be so heartless!
"
Right, that's why while I think that it's a good idea in principle, it'll probably never be done, and almost certainly never be done in a way which is a net positive. The point is to reduce the size of government (in number of regulations, government employees, etc.) and encourage some amount of personal responsibility (at least the responsibility to ask private charities for money if necessary), but instead you're going to end up with a huge mess of limitations and exceptions which would rival the US tax code in size."Oh, I'm already out of money and unemployed but I need to have an emergency surgery done. Would you really be so cruel to not help me? It's just money, I will pay you back, I swear! Don't be so heartless!
"The only way I'd agree with UBI is if part of the money is automatically "saved" somewhere, meaning even if the person receiving the stipend is rather lazy or a spendthrift, he/she would still end up with some savings, which can only be accessed upon reaching a certain age or for medical emergencies.
I'm not so sure about the idea of limiting the UBI by income. That would just bring us back to the same problem we have now with cash transfers to the poor, they reach a certain income level, they lose their allowance, making some people just not try harder.