A person whose name is either unknown or forgotten(noun)
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Use "whatshisname" in a sentence
"Maybe Carter could take a page from your book, call whatshisname an "idiot" and then take issue with something barely related someone else said."
"Although I like the idea Jay whatshisname from Tropic Thunder as Pete."
"She blamed Perez Hilton for her loss in the pageant, she blamed Shanna Moakler and Keith whatshisname for losing her crown, and blamed everybody else for her behavior."