70s or 80s film about a young couple on a crime spree (long before "Natural Born Killers")

Two scenes stick out in memory:

(1) the girl tosses her pet fish out onto the lawn to die

(2) the guy chases her father into a stairwell, saying, "What if I shot you, how would that be? Wanna hear how it sounds?" Then BLAM, he fires it in the stairwell.

Dad's understandably alarmed and runs for it, and the guy shoots him dead anyway.

The girl seems only mildly upset about this, and sort of pokes at his corpse before they skedaddle.