Well, I've had deliberate exposure to CS- in a gas chamber- and it's very not nice!
It can and does induce panic in people who are briefed and expecting to be exposed to it. I guess the effects would be magnified if you didn't know what it was.
On the subject of standing under the wing. I once was starting up at LCY, funnily enough. When we'd got a few started, the start crew told us to shut down. It was a fuel leak from the wing, and as it was a Avro RJ-100, when the engineer got on his steps to fix the leaking MFLI- with his rubber hammer, he did so in full view of the pax on that side.
He gave it a few gentle taps- which didn't work. He then gave it a big prod, which resulted in a couple of gallons of Jet A-1 landing on him! However, this stopped the leak. So he wandered off happily for a clean up. I guess he wasn't going for a fag......
Shortly after this, I found myself explaining the situation to a concerned lady passenger. She wanted off. I said she was free to go. (didn't blame her really). She then said she wanted off, and she wanted her money back.
I explained the aircraft was going to Glasgow now, as she wished it to do when she bought her ticket- so either hop off or stay on, but choose quickly please, so the rest of us can go. She got off..