What made Barney, the purple dinosaur and nineties kids’ TV sensation, so infuriatingly loathsome? Was it his doofy voice and inane giggle, coming at you like a low-watt Pillsbury Doughboy? His menacing rictus and unnerving hat-band strip of teeth? His shameless abuse of nursery rhymes? His indifference to the anxious smiles on his young friends’ faces as they all danced in lockstep to “Indoor-Outdoor Voices”? The short answer is yes, it is all those things, and, as a result, he and his show inspired an acute degree of animosity; a new two-episode docuseries from Peacock, “I Love You, You Hate Me,” dares to investigate.