Green’s Dictionary of Slang

(US campus) a hypocrite, an insincere person.

1975

G. Underwood ‘Razorback Sl.’ in AS L:1/2 58: false face n One who is insincere.

(US society) a bustle.

a.1889		Nat. Police Gaz. (NY) n.p.: The scheme worked to perfection. In the large bustles which they wore, the dudes carried off their wardrobe in large false hereafters, and passed the lady of the house on the way out [B&L].
1890–1904		Farmer & Henley Sl. and Its Analogues.

(US gang) to claim gang membership when one is not in fact a member.

2001

(con. 1990s) in J. Miller One of the Guys 75: ‘We don’t want nobody [...] false flaggin’ with Crips or somethin’’.