I don't participate in FecesBook, but I have heard plenty of funny and stupid things in gun stores...
The most irritating thing newbies believe is that all it takes for someone [who's never shot over 100 yards] to instantly start shoot 1000 yards, is a high-powered scope, and a 6.5 Creedmoor...
Overhearing a conversation at the local gun store between 2 guys around college age. I'm paraphrasing because I don't remember the exact words, but it went like this...
Guy 1: "Do you have any .338's?"
Employee: "Sure. We got a .338 Lapua..." (hands gun to Guy 1)
Guy 1: "One day I'm going to get me one of these, then I can start shooting deer farther away..."
Guy 2: "Hell yeah! How far will it reach?"
Guy 1: "A long way...3-400 yards..."
Employee: Turning red trying not to laugh at their stupidity.
I've had tons of people ask me (after simply bore-sighting their rifles), "Is it sighted in enough to hunt with?"
Watched tons of people at the range hit a paper plate 3 times at 100 yards (roughly 3-5" groups) and confidently proclaim, "Yep, she's good!"
I've had a couple of idiots not know the difference in cartridges and metric caliber sizes, and ask me "Why in the hell do you need a 7mm Magnum to hunt whitetail deer?" Then I ask what they use and they say, ".300 WinMag..."
I've heard tons of them, but it's late and I'm tired, so they're escaping me at the moment.