Self explanatory. After having engaged in sexual intercourse and/or activity, either one or both of the individuals come to an ultimatum in which they terminate the relationship that had brought them to such a level of intimacy. Basically, one of the bastards gets cold feet and walks out on that other bitch's ass.
See Bill run. See Bill run over to Suzy's place for a booty call. See Bill turn into a pussy and give Suzy the good old Fuck n' Dump.