According to the federal reserve website... That clerk can fuck right off. Below is the copy pasta

Mutilated currency is a note that has been damaged to the extent that one-half or less of the note remains, or its value is questionable and special examination by trained experts at the Department of the Treasury or the Bureau of Engraving and Printing (BEP) (Off-site) is required before any exchange is made.

Under regulations issued by the Department of the Treasury, mutilated United States currency may be exchanged at face value if:

More than 50% of a note identifiable as United States currency is present. – OR –

50% or less of a note identifiable as United States currency is present and the method of mutilation and supporting evidence demonstrates to the satisfaction of the Treasury that the missing portions have been totally destroyed. Burnt currency that is clearly less than one-half a complete note, and cannot be handled without compromising its integrity, is considered mutilated currency. Any badly soiled, dirty, defaced, disintegrated, limp, torn or worn out currency note that is clearly more than one-half of the original note, and does not require special examination to determine its value, is not considered mutilated and should be included in your normal deposit.