side, v.² — Green’s Dictionary of Slang

side v.²

to act in a pretentious manner, to put on airs.

1913

A. Lunn Harrovians 47: He waits till he finds him wearing carpet slippers in the yard, and then tells him he’s siding.

sidebust (v.)

(US black) to gossip, to tell tales.

1991

L. Bing Do or Die (1992) 120: Okay — this is Gang Class. There’s no sidebusting in here. Anything said in this room stays here.