Head constable Neeraj Balhara shot dead Pandav Kumar (in red), a delivery executive. ( Two birthday parties, about 80 km apart, have ended in four murders as minor arguments snowballed into rage crimes. In Delhi, a police constable opened fire at a 21-year-old delivery executive, and a gym trainer and his associates in Bulandshahr allegedly shot dead three men during an argument sparked by the smearing of cake on his face. Delhi Cop Turns Killer Pandav Kumar, who worked as a delivery executive for a food aggregator, visited his friend Rupesh Kumar’s home on Friday to celebrate the birthday of his two-year-old son. When Pandav and Rupesh were on their way out to make some late-night deliveries, Neeraj Balhara, a head constable with Delhi Police, started asking them questions. Neeraj, police sources have said, was not on duty at the time. Rupesh has told police that as soon as they told Neeraj that they were from Bihar, he became enraged, and an altercation followed.…