Possible Clues:

• Device for practical joke? Blunder getting person upset
• Practical joke proving social blunder when taken the wrong way
• Perhaps Labour blunder turns into potential embarrassment ...
• One may catch, say, Labour's blunder on reflection
• Schoolboy prank that's the reverse of social gaffe
• Bird catcher's practical joke
• Explosive device in birdcage, say?
• Pitfall
• Hazard for the unwary
• Practical joke producing disapproval by some when upset