When one has simply nothing better to do than masterbate so they choose the easiest thing to jerk off to. They do not necessarily have to be horney, they just can't keep there hands off their dick. A cheap wank is generally occurs when one is just bored and wants to blow easily.
One who has a Cheap Wank will jerk off to what ever gets them going easily.
Harry was home alone so he watched his favourite porno for the sake of wanking.