ITHACA, NY—Michael Pelske changes his bed sheets after every breakup, the 24-year-old bicycle messenger announced Monday. "I'd never bring some woman I just met home to a set of filthy sheets," said Pelske, who changed his sheets Saturday before hitting the bars following his break-up with Linda Keely, his girlfriend of four months. "But then, a few weeks into the relationship, you start to let things like that slide." Pelske's cotton-twill, 180-thread-count, light-blue sheets have been washed 13 times since his mother bought them for him in May 2001.