A few of my favorites from over the years that fall into the category of "General Idiocy." Most of these were things I overheard being said authoritatively:
"There ain't no rattlers in Arizona [sic]"
"If you hike faster you need less water"
"It's better for your knees if you run downhill"
"If we run out of water we can get some from that cactus over there, I learned in the Marines." <-This was a fifty-something man pointing to a barrel cactus and he was serious.
"You should try carrying your pack a lot higher on your back like I do"
"When I'm hiking my arms always hurt before my legs do"
"I hate the fact that you have to go uphill to go up a mountain"
"It doesn't snow up here because the desert all around the mountain is too hot"
"You get out of breath because you are getting closer to Space the higher you hike so there's less oxygen"
"No, a cup of water weights like eight pounds, man!!" Some guy who was mad his buddy was telling him to carry more water.
Here's a few that fall into the "Trail-Specific" category:
"How much further is it to Kitt Peak??" I was asked while hiking the King Canyon trail in the Tucson Mountains.
"Your gun is making my group nervous; it's not like there are any dangerous animals here...any bears or anything!!" this was a sixty-something lady in the Santa Ritas and I was packing my truck up to leave after coming down from Wrightson. I wasn't even parked near her "Group." A few weeks later there was a bear incident on Josephine Saddle.
"Did you know this mountain is actually an active volcano?" -Some dingbat on the Sabino trail trying to impress high school girls.
"I've hiked a few 14ers; in fact, my first one was Mt. Humphreys" -Summit Hut employee who was off his meds.
"They named this mountain after all the trees that used to grow here before the big Aspen Fire." -Some lady near Wilderness of Rocks on Lemmon.
"They call this a sky island because you are higher than the clouds up here." -Some rocket scientist at the Palisades trailhead.
"How much further to the dam?!" -Always asked by some poor exhausted soul on any trip I've made to Pima Canyon. Preferred response: "Which one?"
Here's a few that I get all the time:
"You must be staying overnight," or "You must have stayed overnight." -A knee-jerk reaction I get to the size of my day pack or the length of the hike, etc.
"Why are you wearing long sleeves in this heat?!"
My newest favorite has to be this one from this weekend: I passed a few guys on the Madera trail and one took notice of my SPOT and says to his buddies: "Why does anyone waste their money on one of those?" His friend said something like: "It looks like he hiking alone" and genius replies with: "I know, that's what I'm saying - he's just wasting money to look cool like an idiot."
Meow!)