Stolen Anti-depressants

The humor comes from the unexpected shift in focus. Instead of expressing anger or sadness about the break-in, the person expresses hope that the thief is now happy, which is ironic since anti-depressants are meant to help the person taking them and they are now gone. It's a dark and self-deprecating way to look at a bad situation, twisting a negative event into a hopeful, albeit sarcastic, wish for someone else's well-being.