Too charitable of me, perhaps; but I could see that as hasty over-thinking, rather than outright stupidity (questioner might well realise shortly afterward, what they’d said – and feel highly embarrassed and, indeed, stupid).
Why is that dumb? The first number on my cell phone is labelled “HOME”, but it doesn’t give the actual number.
Mine is this. Before a midterm or final exam I would schedule a question period. It was the students’ last chance to ask about something they might not have understand. The first question, virtually always, was “Is X going to be on the exam?” I always answered “yes”, whether or not.
Teachers are going to win this, mark my words.
Maybe not the stupidest, but my favorite question of all time from a student has to be “Mr. Silenus, how do you spell ‘illiterate?’”
I was born on Easter Sunday. I’ve had not one, but two college-educated adults asked if my birthdate (not the day I celebrate it, mind you, but the actual date) is different year to year. And no, they weren’t joking.
I was also asked “The flyer says that [monthly event] is always held from 12-2pm. Does that mean tomorrow’s session starts at 12pm?” I was flustered and told them yes, 12pm EST (which was also in the flyer) because I couldn’t think of any other reason they would ask that.
I think it’s more similar to:
-I don’t believe in Santa Clause.
-Aren’t you afraid of not getting any presents?
If asked, “Aren’t you afraid of going to hell?”
What is a response to this other than telling them to slap their forehead? My response was to laugh and ask, “Think about that for a second”, then walk away.
That’s true from your own perspective, since you know the strength of your conviction - you presumably think that the existence of God is as likely as the existence of Santa Claus. In essence, that’s all that the questioner was enquiring about - the strength of your conviction.
I think you have to take cultural context into account in deeming a question “stupid”. A vast number of people do think that a consequence of atheism is risking damnation to hell.
It seems to me that you’re calling the believer stupid for failing to see things from your perspective; when you are doing precisely the same thing - failing to acknowledge that from the believer’s perspective this was a reasonable question.
This isn’t different than:
-I believe in God and therefore have to follow religious restrictions issued by Him.
-Aren’t you missing out on a lot of fun?
Was it? By this rational, should my response be more along the lines of, “Aren’t you afraid you’re wasting your whole life praying to something that doesn’t exist?” From my perspective, this is a reasonable question.
If I asked that question after being told the person is a theist, I think calling me stupid is fair.
I really think many of the questions in this thread aren’t dumb or that dumb, and if they are the dumbest that Dopers have encountered, that most of you have interacted with a fair/reasonable circle of society. 
Missed the edit window.
Didn’t they do the same thing? Didn’t they fail to see MY perspective when asking about hell? In my opinion, it’s a stupid question because of THEIR failure to see my perspective.
You have (to my mind) a rather odd definition of what constitutes a “stupid” question. If somebody has a completely different worldview to me, and the consequences of that worldview are strange to me, I don’t think it’s “stupid” to enquire further. Personally, I would treat it as an opportunity to explain why my beliefs don’t entail a fear of hell, rather than to condemn the question as stupid.
ETA: A “stupid” question is, to my mind, something like “if we evolved from monkeys, why are there still monkeys”, when asked by anyone over the age of 18 who has a conventional education and access to a computer. It’s stupid because it’s based on willful ignorance. The fundamental misconceptions that are entailed have been patiently explained an nauseam, and can be found in 5 seconds online. It’s stupid when you willfully refuse to even try to understand your opponents’ position in an debate.
I rest my case. 
My friend was driving while we were approaching the airport to drop off another friend so he could catch his flight. The road forked with the typical signage denoting “arrivals” or “departures”. My friend driving was in the lane for arrivals so I alerted him “whoa, whoa, whoa, you’re in the arrivals lane.”
He asked “Why would I want to go in the departures lane if we haven’t dropped him off yet?”
I have some deep scars on my chest. I was wandering around a shop once, and the clerk looked at me and exclaimed “wow, are those autopsy scars?”
I just stood there and blinked for a minute while the full import of that question sunk in.
However, to be fair to the kid, ever since then I’ve been telling inquisitive morons that they’re autopsy scars just to see the look on their faces. Thanks, random clerk with the stupid question!
I was asked many times over the years if zero was odd or even by my students.
-College students.
-Juniors and seniors.
-In Computer Science.
-You know, the field with binary numbers that have an trivial test for odd/even.
These people wrote the code in programs you might use. Ever wonder what it’s crap?
You have a very strange idea of what a “stupid” question is.
Not a dumb question at all, I don’t know my work number, I have to look at my business card to look it up.
He said he called him up to ask this. That would seem to imply that he called the very number he was asking about.
Not a stupid question. Since division by zero is undefined in mathematics, it’s reasonable for coding beginners to ask if zero has other special qualities as well. It may not be obvious to rank beginners that they just need to check the last binary digit.