I did this now and then where I was volunteering, which is how I heard my boss badmouthing my depression as he was standing directly behind me. Ended up just quitting entirely very soon after, in part just out of a still-lingering sense of betrayal. He'd always been pretty great to joke around with in general, and my ass really thought we were on good terms for some reason. So. Don't eavesdrop unless you're ok with what you hear, I guess.