I was attempting to send a calling card to another user through IM. Instead of selecting a calling card from Inventory, I clicked on the username in the Friends tab, then dragged and dropped it into the IM chat box. Doing this caused the viewer to crash immediately. A second attempt to perform this action lead to the same result.

I don't know if this is considered an "unauthorized" action, but the viewer doesn't stop it from being performed, and the cursor shows a "drop item" icon instead of a "not allowed" one.