YTA. Of course he's not entitled to your money, but he is your friend, his life is about to be ruined and you have the power to save them.
What happens if you lend him the money and he doesn't return it? Your budget for a vacation is smaller. Doesn't seem like the worst thing in the world.
What happens if you lend him the money and he returns it? (80% is a really big percentage,man) You save his life and also go on vacation. Win win.
What happens if you don't lend him the money? If you were a good person i would like to think you would help him find someone is willing to lend it to him. If not, you are just throwing him under the bus. If you were in his position, wouldn't you like someone to give you a hand?