Question: What did Walter mean by, "You're killing your father, Larry!"?
Question: What exactly was Maude's doctor checking for? That he was fertile? That he didn't have an STD?
Answer: As it's not specified, any answer would be speculation. An STD check would be fairly straightforward, and definitely something Maude would want to know about, so we can assume that was part of it. And even though the only way to check if he was fertile would be to take a sperm sample, which might arouse suspicion in anyone else, he asks Maude about the doctor immediately after she reveals that she slept with him with the intention of conceiving, so it's implied that this was performed as well.
Answer: Maude wanted a strong, healthy man to conceive a child, so she sent the Dude to her doctor to be sure.
Question: Why is the dude lying and telling Jackie Treehorn that the amount of the ransom is only half a million dollars? Thus, he also cuts in half his own commission.
Answer: He's not talking about the ransom, he's talking about Bunny's debt to Treehorn, which is half a million dollars. His commission is 10%, which gives him $50,000, far more than the $20,000 he'd been promised by The Big Lebowski.
Question: Did the nihilists force that one's girlfriend to get her toe cut off?
Answer: They don't appear to have; she's a nihilist too, and seems to have been in on it. The way they put it in their confrontation with the Dude and Walter suggests this: "His girlfriend cut off her toe", "She thought we would get a million dollars." Both expressions imply that she did it herself in the hopes of getting the ransom.
Question: Someone suggested that Donny sitting down after missing the strike was due to it having been the last of three throws. Wouldn't that mean that he missed a perfect game by just one pin?
Answer: Not necessarily; even if one doesn't have a perfect game going, one could still bowl two strikes in the tenth frame and thus get a third throw. Given his reaction, we could assume he came within one pin of a perfect game, his final score now being 299, but we can only speculate.
Not necessarily; even a player that doesn't have a 300 game going could bowl three in the final frame.
Answer: Generally, he means that the boy, Larry Sellers, is disgracing his family (Walter has huge respect for the boy's dad, but considers the kid a dunce). Specifically, Walter is blaming Larry for his father struggling to breathe; that's Larry's dad in an iron lung in the background. Walter and The Dude become louder, more insistent and more vulgar, but the kid still blankly refuses to answer, and all you can hear is the iron lung pumping in the background. Frustrated because the kid isn't intimidated, Walter lashes out: "You're killing your father, Larry!"
Charles Austin Miller