In my current game, I accidentally overspent while instant buying some NLCs and ended up at -2000. It's late game and I'm way ahead, so I thought rather than selling tech or ships to get out of debt, maybe it'd be fun to try to mooch or bully the amount out of the other races (relations with them varying between neutral and friendly).

So I pick a minor race, the Carinoids, and start requesting some bc's as a handout. The trade dialog is green, so I run the number up to just before it turns red and hit ok. (I assume that means they'll agree to give it to me.) After hitting OK in the money popup window, tThe trade window text turns white, and I hit send. The AI shows a reply like "it's always me me me with you" or something (though I've never asked for a handout before and have given this race a few small handouts), and no money has been given to me. I try again, requesting a lesser amount, and get back another complaint and no cash. Try again, with an even smaller amount, and get told "Didn't we just give you money?". Umm, no, you didn't.

I then tried with some other races, and saw similar behavior that if they rejected the request (requests that were always green-lighted), they still acted like they had given it to me.

So it looks like:
1 - The red/green highlighting doesnt correctly show you how much of a handout you can get
2 - When a handout request is rejected, the AI still treats you like it gave it to you.

Also, I really would have liked to be able to phrase the request more as a demand/threat rather than asking for a handout, (I think this is keyed off your current relations to that race) but there doesn't seem to be a way in the game to adjust those relations exept by declaring war. So if a race I want to bully likes me, we have friendly relations and I can't threaten them.
It'd be nice for the player to be able to set the relations level of how each race is treated by us, so even if a race likes us, we can dislike them (or vice-versa if you're trying to improve relations).

As for the miserable Carinoids, they would pay for their insolence: I tried to check the trade embargo to deny them the 77bc trade income they were getting from me, but the box wouldn't stay checked. So instead I obliterated their starbase and puny defense fleet, and they then gave up their sole planet in exchange for getting a peace treaty.