Apparently astronaut Young didn't realize his microphone was on

http://www.hq.nasa.gov/alsj/frame.html
(1. click "Apollo 16" link
2. then click "Debrief and Goodnight" under "The First EVA" under the "The Journal"
3. look at around 128:50:37
at around 128:53:58 he's informed about the hot mike )