Coming back from our ITC in Korea, Japanese TSA agents pulled me aside after the initial x-raying was completed and were interested in two items: my old primary light battery (aka, the "dynamite stick") and the Gillette shaving cream canister that classmate Ali (from Dubai) had left with me. It was written in Arabic, you see, and nothing upset them more than a terrorist alphabet!
I offered to shave in front of them to legitimize the product, but they'd seen one too many Mission Impossible movies involving weopons-concealing shaving cream bottles. After letting three different agents try to unscrew the bottom of the supposed fake canister to no avail, they finally let it through.
The light battery wasn't so lucky. Being old, there were no manufacturer stickers on the shrinkwrap proclaiming "Yes, this is an NiMH battery", so they asked if I wouldn't mind them cutting it open. Well, yes, I minded since I didn't own a shrinkwrapping machine at home and I kind of like my gear the way it is thank you, but yes, if it would mean making my flight then fine, sure, go ahead.
Upon inspecting the contents of the shrinkwrap, however, seeing the cells and the plates connecting them, they were not convinced. "It doesn't say 'NIMH' anywhere on these batteries, so we can't verify that these are safe for travel." I reminded them that I was on a return flight, having passed through this very airport (and many others through the years) without incident. I asked them to consider the thousands of dollars of other dive gear surrounding the light and what kind of plot they think I was hatching involving drysuits and deco regs, but once you start suggesting these sorts of things and using keywords they're trained to flag even if it's to call attention to the absurdity of the situation, their retard antennas start tingling and they get stubborn.
In the end, the only option left to me was to ship them via a land-based shipper to my in-laws up on the mainland (I've never been happier to call my in-laws than I was that day). Then I turned to the TSA agent and said, "You realize that I will turn around and ask my in-laws to ship them down to me by air freight the day after they arrive, right?" to which the agent replied, "Well sir, at least it won't be our airport."