1 Monty: Well, if I want to save dad, I guess I have to try one of these.
2 Monty: This is the cup of a carpenter!
3 Monty: {takes a long drink}
4 Knight: You realise you could have given that to your father without risking your own life as well?
4 Monty: Now you tell me.

2012-02-29 Rerun commentary: Yeah, a plot hole that always bothered me in the movie. His father was dying anyway. Why did Indy risk his own life to test the Grail, when he could have just tried it on his father first? If he chose correctly, it's all good, but if he chose incorrectly, his father would die no matter what he did, so there was no point in trying it himself.

Of course it was a stressful time and maybe he simply wasn't thinking that pragmatically. He wanted to save his father more than anything, so putting himself in the firing line first, so to speak, isn't that much of a stretch. But still.