Pam encouraged Jim to do impressions of co-workers in the office. They both did the same impression of Stanley at the same time and she called "jinx." The rules of jinx meant that Jim couldn"t talk until he bought her a Coke; only all the Cokes were sold out.
Dwight informed everybody that he had called drug testers into the building to see who had left the half-used joint in the parking lot. Michael cancelled the drug testing because he feared the pot he inhaled from a girl's joint at an Alicia Keys concert the night before would show up on his drug test.
Michael called the staff into a conference room. He wanted to teach everybody about the dangers of drug use. Jim was still jinxed from talking. Pam didn't believe Jim would remain silent the whole day. To her surprise, Jim's silence was mistaken for emotion by the other co-workers.
Michael confessed his fear of the drug testing to Dwight. Dwight stepped up and submitted his pee test as Michael's. Angela did not approve of this scheme. Out of guilt about cheating the law, Dwight turned in his resignation to the sheriff's department. Michael granted Dwight the title of the branch's official security supervisor.
Pam bought Jim a Coke to buy back for her so he could talk. She told him she found it hard to imagine a whole day of not talking to him. Especially a day when Dwight was in a sheriff's uniform, carrying pee around in a cup.