As much as I have heard this line several times in my teaching career there have been many others that I think top the list for best excuses for in completed work.
• My brother ate it
• My gerbil peed on it
• My dad spilt his beer on it
• My mom cleaned it up on one of her cleaning frenzies
• The wind picked it up and it flew away
• My cat put it into its litter box
• It simply disappeared
• I left it at my soccer tournament
• You didn't get it? Maybe your lost it!
Regardless of the excuse I don't think there is ever a perfect response but as usual I am ready with a sarcastic remark like:
• Did your brother enjoy it at least!
• Was it that bad that your gerbil had such a nasty reaction?
• Cheers to your dad for reading science in his spare time
• Can you tell me the science behind how your project could fly away like that?
• Magic is an interesting phenomenon can you make your project reappear as fast as it disappeared?
• Science is everywhere and now so is your project
My motto in teaching is "Don't stress about it!"
I have found that no matter what the excuse is, getting angry does not make the assignment 'reappear'. Students now do much of their work in class and we avoid that step of bothers, dads, mothers, gerbils or natural disasters getting involved with their science masterpieces.