Likewise, I've flown more in the last year than in the decade prior and every single leg my Flipper has been in the side pocket of my backpack. Never once has it received even a second look from the TSA, including also DEF CON.
That's of course not to say some rogue agents haven't confiscated a few Flippers, especially after seeing hyperbolic media reports about them being magical evil hacker devices, but I have high confidence that there's no official policy to do so.