I keep seeing people say that the underpants talk, but I haven't seen that in-game. Am I missing something? >_>
Prior to today the Kickstarter pants had no voice associated with them and the "talking" would appear as brief text over your character's head. Without the audio (and the fact that it didn't show up in the chat-log panel), it was extremely easy to miss. It didn't help that the comments are few and far between.
Today, however, the patch added the missing audio to the pants and it's obviously easier to tell when they're talking to you. They don't speak very often, though - only when you do specific things.