A straphanger was slugged in the face by an irate seatmate on a Manhattan-bound subway, but he managed to wrestle the “little b–ch” to the floor — but that’s when fellow passengers jumped in to help his attacker. Alexander Rakitin, 42, was riding the N train to his Manhattan finance job Monday morning when he sat down next to 34-year-old Timothy Barbee. As the train took off, the car jolted, causing Rakitin’s knee to jostle Barbee’s — which set the alleged assailant off. “He was just very aggressive. I’m like, saying, ‘Dude, just chill, it’s like 8:30 in the morning....