Biffing

If someone is "biffing" they are lying or exaggerating about a situation. It can also be used by calling someone a "biffer" if they are known to lie.

He's a big BIFFER, ket sniffer, clit flicker.
Oi! Quit biffin you little rapscallion!
Mum's comin' up da stairs! nah, quit biffing bro.