A guy comes in to my work.

Guy: My telephone ringer isn't loud enough. Do you have anything louder?
Me: Sure, right over here.
Guy: ...but my sister got your model and it wasn't loud enough for me.
Me: ...

If our model isn't loud enough, then our model isn't loud enough. It's called the Transitive Law, grandpa.

Different Guy: Wow, do you have one that does video too? How many megapixel is this? How much memory does this have? What kind of memory does it take? How much memory does it have? Where do the batteries go? Does this have the new USB "two point oh?" So this whole project would cost me about $200, eh? How long will this be on sale?

Keep in mind that every question he asked was either unimportant (who gives a shit where the batteries go?) or the answer was printed on a nice big card right in front of his big fat face.

Look, I'm sure you're a nice guy but I really don't feel like playing foil to your monlogue. Come in, ask me some intellient questions not designed to make yourself feel up to date on all the newfangled shit and get the fuck out of my store.

Last, but most assuredly not the least of my trials today is a guy who wants to take two huge-as-fuck speakers, attach a 1/8" (headphone) jack to 'em and then plug them in to his computer.

Me: I don't think that'll work.
Speaker Guy: Why not?
Me: Because your computer is expecting to drive some headphones with that, not real speakers.
Speaker Guy: But there are two holes in the card, one with a headphone symbol and one with a speaker symbol.
Me: Ok.
Speaker Guy: [obviously dying for a good argument here] But ...wouldn't the different symbol mean I can plug in a speaker?
Me: I doubt it.
Speaker Guy: ... But then why would it have a different symbol?
Me: I don't know. [thinking to myself, "there's a reason that amplifiers come in big metal boxes with big metal transformers, genius."]
Speaker Guy: So I should be able to do it this way.
Me: Ok.
Speaker Guy: [clearly miffed] Well I should be able to do it, right?!
Me: I don't think so.
Speaker Guy: Well I do!
Me: Ok.
Speaker Guy: [head nearly explodes]

Next customer. Not kidding.

Cellphone Guy: This phone doesn't get good enough reception where I live.
Me: Ok, we can take it back.
Cellphone Guy: How about one of these phones?
Me: I suspect you'd get better reception with this one.
Cellphone Guy: How could I find out if it worked better?
Me: You'd have to buy it and try it out.
Cellphone Guy: Well that's silly.
Me: ... How else do you suspect we find out? I don't know of too many stores that let you leave with stuff for a few hours.

Yes, I actually said that to him.

Me: Do you have any alternate ideas?
Cellphone Guy: ...no...