Spikeletz, which are apparently a hot trend in the pre-teen community, are silicone rubber bracelets with countless little flexible spikes:
I discovered them in a toy store when I was buying a present for my niece, and bought a couple.
These are AWESOME fidgets. They kind of tickle me if I actually wear them on my wrists, but they’re SQUISHY and soft and tactile-ly interesting. The rubber spikes taper quickly to a hair-like width, so they give a tickling feeling if you touch them lightly and a nubbly feeling if you press on them. The rubber has a sort of velvety texture. Squishing the whole bracelet around in your hand also makes a satisfying rubbery sound.
Most of these are neon-colored and are therefore not that great for super-conservative environments, but as you can see above there is a black-and-white version that might potentially “pass” for an adult fashion statement.
If you can handle wearing them around your wrist, they’ll probably fit just fine, as they’re on elastic bands and appear to be sized for more or less adult wrists (I’m guessing they’re marketed toward teens and tweens).
If you can’t find them in a nearby toy store, they appear to be available online through the manufacturer’s website at Optari.com, for about $5 each.