Sabandija is literally vermin (Collins)and metaphorically wretched/louse (Collins) or "persona despreciable" (Real Academia). However wretched/louse seems probably too old-fashioned so I have given a more modern equivalent.
"Tienes cara de" is literally "you have the face of a ..." which I have given a more native English sounding rendering.

You seem to be a scumbag
You appear to be a scumbag
You look like a scumbag