I've carried one for years (albeit I am an infrequent traveler) and there have only been two times it's drawn the slightest attention from security.

#1 was a family emergency trip where I packed *VERY* quickly, I simply threw what I thought I would need in a bag and headed off to the airport to see what was flying. (This was before the internet and it was a short hop with lots of flights.) Since my bag wasn't completely full nor properly packed things shifted and all the electronics (and especially the charger wires) ended up in a pile which of course took an eyeball. The toothbrush wasn't singled out, it was just part of the pile.

#2 was PVG, the x-ray gal asked about seeing what looked like two toothbrushes in my bag. I pointed to my wife, "two people, two toothbrushes" and that was the end of that. The bag was never opened. (Note: China's airport security is *MUCH* more friendly than the TSA. Even when my SIL lost a prohibited liquid the screener was apologetic, not hostile.)