I tend to stay inside when the temps get into the 55F or lower. There is a reason I moved to the desert.
When I visit my son up north for Christmas, I expect to suffer - but gladly.
When I get into a bad state, I have to walk it off outside. Saturday I was in such a state and walked outside for over four hours in the 20 degree temps with wind chills in the signal digits.
Just a few days ago I was out blowing snow at 14F and 35 mph wind, that was cold!
Wow. I don’t like the cold, but the average high temps here are below 65F for eight months of the year (this cite says the average is only above 65 two months of the year, but June and September have decent odds of breaking 65), so it would be absolutely miserable if you lived here. Only visit here in the summer, ok?
While in the USAF, I was stationed in Minot, North Dakota (at that time a SAC base) and when I first signed on to my Squadron (they later transferred me to Crypto) I had to stand guard with some B-52’s.
It got down to 30 below some nights!
Me and this other guy took turns in the shack with the heater in it?
And he always left me a fart.
Sucks to be me, I reckon! 
Q
It depends on what I’m doing, but if I’m just going somewhere, there’s no such thing as too cold as long as the cars work. Yesterday I went to a bar at -35* C (without windchill) with a light jacket and it was fine (except for the time I grabbed a doorknob with a bare hand). Not everyone here shares the same views, because the place was dead compared to usual and I felt a little bad for the band.
It’s too cold too often here in Saskatchewan to let the weather win. I try to not let it stop me from doing stuff as much as possible. I can’t drive my motorcycle though 
That’s it - if we only went outside in perfect weather, we’d spend most of our lives inside. As I mentioned in another thread, the malls were full this weekend - we have systems set up to deal with this cold weather, and we just adapt. Everyone has block heaters in their cars and a place to plug in, we all have parkas and winter boots - it’s a pain in the ass to deal with cold weather, but life doesn’t stop because of it.
Anything less than 50 and I start canceling plans. I live in California, so sue me 
It really depends on the wind. I can do alright walking around anything in the double digits so long as I’m dressed reasonably and it’s a still day (night). Add a wind and I’d say 20F or below will have me swearing a bit.
:DSpent four and a half years as an undergrad at North Dakota State University in Fargo; learned a lot about cold weather. One winter I went for a long walk when it was around -20F, just for the hell of it. I didn’t get frostbite or hypothermia, but the surface of my legs was pretty cold by the time I got back.
When temps got well below zero like that, friends from rural ND and MN cancelled plans to go home for the weekend. If your car crapped out or crashed on a well-traveled interstate highway you’d be found/rescued in short order, but if you ended up in a ditch on some remote rural highway, there was a fair chance you’d freeze to death before being found (this was in late 80’s early '90’s before cell phones were common).
When I went to UW-Madison for grad school, the climate was slightly warmer; I remember laughing at the evening news when they spoke of firefighters “braving 20-degree temps” to fight a fire. 
More recently, in April 2005 I was returning to Michigan from a motorcycle trip down to the Smoky Mountains (eastern Tennessee). The weather was crap all the way home:, rain, sleet, and temps hovering in the low 30’s. With heated handgrips my hands remained functional, and with an electric vest, I wasn’t becoming hypothermic - but by the time I reached Michigan, my legs had become oddly cold. You know how when your lips get cold, you can’t speak properly because your lips won’t move as fast as you want them to? That happened to my legs. I stopped for gas, and was having difficulty walking because my legs were so goddam cold they couldn’t move at the speed I commanded them. Strangest thing. I guess that’s what 33 degrees and a rainy 70MPH slipstream does to you. :eek:
As for the OP’s question - how cold is too cold - depends on what I’m doing outside. Wife and I don’t go for pleasure walks when it’s below about 50F. I don’t go for pleasure cruises on the motorcycle when it’s below about 45F; I will ride when it’s colder than that, but only to get somewhere (e.g. home from a trip). I can be outside when it’s much colder than that; if the driveway needs shoveling, it doesn’t matter how cold it is, you just bundle up and head out.
It is -29 C here this morning, -32 C at the airport. This is nearly as cold as it ever gets here (Calgary), though people always seem to remember the last cold snap as “-40”. I dont think Ive ever seen actual -40 in the 30 years I have lived here, upper -30’s maybe.
I have some outside work to do this week but it’ll get close to zero by the end of the week and I will wait till then. At -30 you have to bundle up very thoroughly but it is do-able. Ever thing is bulky and awkward, wet frost builds up around mouth and nose, glasses fog up, a few minutes of stillness and you are too cold a little work and you are sweating. Still manageable though.
I find -10 quite pleasant to work in, do a lot of backcountry skiing / camping and -5 to -10 is better than close to zero because you stay nice and dry. And the powder is fluffy.
Its all about having the right gear to be comfortable. I did a weak of work in -39C up north. Wearing insulated coveralls, goggles, etc, it was quite manageable.
My son and I went on a campout with his Boy Scout troop this last weekend. The overnight low temperature on Saturday here in Connecticut was 13 deg F. Yes, it was very cold, but we had the gear for it.
We both had 0 deg F rated sleeping bags, sleeping bag liners, and insulated ground pads. Inside our bags, we were toasty warm. Our faces were so cold, though, that our noses ran all night. It also sucked when you had to get up to pee, which always seems to happen when all bundled up.
The coldest temperature I’ve experienced was up in the Arctic when I was in the Navy. The outside temperature (in April) was about -10 deg F most days. The first time I left our submarine and went out onto the pack ice, it didn’t feel particularly cold because the sun was out and there was no wind that day.
Somewhere around -20F, probably a little colder. I mean, certainly, I’ll be RELUCTANT to go out anytime it’s below about… oh… 10F, but it has to be pretty darn cold to keep me from walking where I need to go.
Yep, totally depends on what I’m doing. Driving to work, but need to scrape off the car and such? I’ll wear my winter dress coat and driving gloves only, sometimes a hat, with the work shoes, even in -30 (admittedly, it sucks, a lot, but it’s for a short time. Then I’m in the car, and while still cold, it’s light-years warmer than the outside). Shovelling at the same temp? Then it’s highly bundled up, longjohns, two shirts, sweatshirt, two pairs of socks, the whole deal.
I’ve been skiing in 0 degrees for hours (mostly tosty), sat in Lambeau for a hockey game in the 20s for hours (warm and toasty), and running to my car and back to work for minutes (mostly freezing). All depends on what I’m doing, and I’ll dress properly for it.
No limit. I find it quite thrilling to walk about in extreme weather.
I was working for the whole of last winter at Oliktok Point on the coast of the Buford Sea.
It never really got above -30 f
Over -80 wind chills were not to uncommon. It had to be -60 f regular temp for someone to even say anything.
It is fantastically cold though. I would go out in a t-shirt and jeans to test my limit. It was about 1-2 min or so. I would continue to get colder it seemed for another min after stepping in side. And I read aobut water freezing instantly if you throw it up form a cup.
Well what happens is if you take a cup of hot coffee and toss it straight up it just turns into a cloud and drifts away. Kinda strange. I did not try it with cold water.
Here’s a guy doing it with boiling water at -40F in Ely, MN.
To much water some of it came back down. Smaller amounts produce a cooler/differnt effect.
I have to say that wind is the worst for cold weather
Without wind I’d rather stay indoors at anything below -50 celcius, though I have walked 45 minutes in that type of weather in just jeans, t-shirt, socks and sandals.
With wind…I’d rather nothing below -30 celcius though I’ll still leave the house long as it ain’t colder than -50.
At -20F we went into a friend’s garage (still air) and blew soap bubbles. They’d rise at first because your breath inside them was much warmer than ambient, but in short order they’d cool and sink, with the soap film freezing solid on the way down. They’d crash to the floor and crumple like a wad of super-thin plastic wrap.
Reminds me of one day when I went outside to blow soap bubbles. They didn’t go up or down, just sorta drifted away and deflated then fell to the ground like wads of super-thin plastic wrap. I’ve never figured out how to reproduce that.