Green’s Dictionary of Slang

(US campus) to make a mistake.

1986		Eble Campus Sl. Nov. 3: faux – make a mistake: I really fauxed that time.
1996		Eble Sl. and Sociability 77: Other borrowings are more complicated. Faux /fo/, a clipping of faux pas, is a noun or a verb: [...] ‘I really fauxed that time’.