i always used my own earpiece on the 320/330 but always plugged in the one onboard before I left. The only thing worse was to walk into the cockpit and find a full trash bag. At my old job, the captain had to sign the logbook so it was easy to find out who left it. I would take the bag of trash and stuff it in his mailbox with a note saying "you left this on the aircraft , I thought you might want it"