Surveillance video shows a man and woman demanding money from the register last week in Chicopee, Massachusetts.
The woman swiped at the worker with a knife several times, but he moved away without trouble, giggling the whole time.
After pressing random buttons and shaking the register, the pair gave up and walked away.
The clerk, who says he found the whole thing ridiculous, wasn't hurt.
Police are still looking for the would-be robbers.
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