What limits should there be for pranks?

The news coming out of the UK right now is that the nurse who took a prank call from an Australian radio station about the Duchess of Cambridge being in hospital has taken her own life as a result of it. This has led to me thinking about what actually constitutes a prank and how much thought tends to go into them in the first place?

Thinking about the call that they made (where they pretended they were the Queen and Prince Charles and got updates on her condition) clearly they would have no way of knowing that this would happen, but would it not have crossed their mind that somebody may have lost their job at least over it?

At what point does a prank become more serious? How much responsibility does the media have in thinking through pranks in general before going ahead with them? Where is the line that should not be crossed?