To point something out in amusing fashion. Originates from the north west of england.
Oh geoff, deeks that fuckin' mare ower theer.
(I say geoff, did your fantastic eyesight permit you to peruse over the visual delight of that nearby female stunner?)
Cumbrian #1: Fancy a ball and biscuit?
Cumbrian #2: Eh?
Cumbrian #1: (While whipping his bollocks out and laughing) DEEKS!
Cumbrian #2: Ahhh you fuckin twat!
Deeks him with the face.