An FBI agent on Queens stakeout clapped handcuffs on the wrong man — a uniformed city traffic enforcement agent who wrote him up for parking illegally, the traffic agent and law enforcement sources told the Daily News. Traffic agent Dipankar Dipu said he was still nursing an injured shoulder four days after his Sunnyside clash with fuming fed Kenneth Diu, who was parked between a metered spot and a bus stop. “I can’t say what made him react so unprofessionally,” Dipu told The News on Saturday. “I was just doing my job. Why he assaulted me and humiliated me in...