For anyone accustomed to bringing some reading material along for a leisurely bathroom visit, here's one to grow on: According to the Post, a man was beaten up Friday night by three other young men furious about his lengthy occupation of the restroom at a Greenwich Village bagel shop. When 23-year-old Zaaven Castelan finally abdicated the throne at Giant Bagels on University Place at 10 p.m. Friday, he found three "pissed-off" perps waiting. Police identified them as Osman Jalloh, 19, Mohamed Sow, 21, and Amadou Diallo, 21. Cops say the three pummeled Castelan when he exited the bathroom, and ran; they were apprehended soon after the incident. Reached by phone, an employee at Giant Bagels insisted he knew nothing about the incident, but added that only works during the day.