One way phone sex consists of a person either calling another person or answering the phone while masturbating. Extra points are awarded if an outgoing call is placed to a friend's significant other.
Carly: I think Tom tried to have one way phone sex with me last night.
Sam: Why do you say that?
Carly: He called and said hello then just started to breath really heavy, but I hung up in time.
The police. Contrary to a popularly accepted best guess, this North American black / hip-hop slang term did not derive from the idea that one should only look once and not double-take at the police (arousing suspicion). Instead, it derives from the first few words of personal anecdotes involving the police, often shared while socializing at BBQs etc: "One Time, I was just comin out the Korean store, and the five-oh seen me..." It became a fun slang device to simply refer to police encounters as "one times," as in "that was close! we almost had a one time." which simply evolved into calling the police "one time." This was very early 90s and only really persists among fans of rap produced in that era.
nigga yo ass bess get yo shit up out here nigga! one time straight flossin this hood f' yo ass. and that's only real, on my life nigga.