In my observations, it depends on the context of the situation.
Most of the time (in my opinion, from my experience), however, if they use the word 'would', they are likely upset, uncommonly perplexed, or emotional because you asked 'that' (especially if they say 'Why would you even ask that?' or if they put uncommon emphasis on 'Why', 'that', or 'would'). They may just be slightly emotional, or find it funny that you asked (pay attention to see if they're smiling or laughing). Maybe you asked something unusual that a native English speaker normally wouldn't say (which may or may not have anything to do with language, and everything to do with culture). Listen to their tone of voice, as it may convey more meaning than the words they say.
If they're calm and collected, however, they might just be more inquisitive and not at all offended, alienated, or tickled by what you said.
Arguably, they could mean the same things I highlighted above if they said 'did' instead of 'would' (especially if they add emphasis somewhere), but I think that's less common (although it still happens).
In another light, 'would' isn't limited to the past, and it's not limited to something that actually happened, while 'did' is. You could ask someone why they would do something they're hypothesizing about, but you can't sensibly ask someone why they did something they're hypothesizing about unless they've actually done it:
- Why would you build that time machine [you're thinking about building (which time machine you've never built to date)]?
- Why did you build a snowman [last winter]?
- Why would you say that [thing you're thinking about saying, but haven't actually said]?
If you actually did 'ask that' and they still say 'would', they might be thinking it's something you're likely to ask again, or be in a habit of asking (but they might not be thinking either of those things).
Arguably, the two phrases are interchangeable with pretty much the same meaning in some contexts:
- Why would you ask that [thing you asked in the past]?
- Why did you ask that [thing you asked in the past]?
Although the words 'would' and 'did' have different meanings, the sentences as a whole pretty much mean the same thing here in some contexts. Saying 'Why would you ask that' seems to me that it would solicit a variety of reasons, potentially, while 'Why did you ask that?' seems to me that it would only solicit one reason (the specific reason you had for asking). 'Why would you ask that?' seems more polite in my mind, because it allows people to answer truthfully without forcing them to say their true intent in that specific circumstance; however, if you know they really only want to know that reason, you probably shouldn't let them think that was it if it was just a reason you might have, but didn't use.
Firstly, let's tackle the use of the phrase "you know everything there is to know about me" and ignore the word "else" for now.
It would be equally grammatically correct (and not really change the meaning, either), to say "you know everything about me." In this context "there is" is basically synonymous with "that exists."
You know everything [that exists] to know about me.
So, reworded, this means of all the things there are to know about me, you know every single one. This is obviously the same meaning as just saying you know everything about me. It is, however, a slightly more emphatic way of saying it. Generally the more words you use to express the same meaning the more emphatic you'll sound. So "you already know every tiny little thing there is to know about me" sounds even more emphasized (and, in this context, more aggressive, too).
So the other half of your confusion seemed to come from the word "else." "Else" needs to refer to something, and in the specific context of this sentence, ought to refer to the only thing the listener didn't already know (or still doesn't). It's easier to see why it's being used when the thing it's referring to is in the previous sentence.
I'll leave you instructions on how to prepare the side-dish, but you know everything else [about preparing this meal].
Here the "else" is all the meal preparation other than the side-dish.
Do you really not know my favorite color? How is that possible? You know everything else there is to know about me!
Here the "else" is everything about the speaker other their favorite color -- which brings us back to the context you provided.
Without knowing exactly how the conversation went prior to this sentence and only having the vague context it's a little hard to say exactly what the "else" is referring to. It sounds like she may have just asked him a question, such as "Would you like some sugar in your tea?" or perhaps "Why are you upset?" and he responded with this, meaning she already knows all facts about him other than this, and thereby implying she should probably also know whether he takes sugar or why he's upset. There is a little wiggle room here since he's obviously being sarcastic and refusing to come out and say what he actually thinks, so he may even be referring to everything other than the fact that he doesn't like horse racing.
Regardless of the words he picked, what he's actually saying is, "You are acting like you know more about me than you actually do, and I want you to realize that."
Best Answer
"Why else" is a common construction in conversational English, meaning, "for what other reason". Read that sentence as "For what other reason would they have a wet bar?" This is a rhetorical question, i.e. a question that has only one possible answer, used to prove a point. There is a wet bar in the limo, so if it's not to provide drinks, what other purpose could it have? One could say this is rhetorical use of Occam's razor; Mandy uses it in a cutting manner.