The telephone lineman or repairman's test set was invented by Mr. Buttinsky. It is also called in the field a butt-set, butt-in set, butt-out set, or just a Buttinsky. The telephone lineman/repairman could clip anywhere in the pair to test the operation of the line and literally butt in on conversations and take control of the line.
The telephone repairman used his buttinsky to isolate the open pair.
Miguel: Did you like Superbad?
Carlos: Yeah dude it was sweet except the bloody jeans part was sick.
Moberry (From out of nowhere): Who has bloody jeans?
Miguel and Carlos: Moberry you're such a damn buttinsky.