Kick Someone When They Are Down Meaning

(idiomatic) To make things worse for someone who is going through a difficult time.

Example: 2000, Richard Carlson, Don't Sweat the Small Stuff for Teens: Simple Ways to Keep Your Cool in Stressful Times, page 114
  They would never kick someone when they are down or give themselves an unfair advantage by cheating or stealing. The implications of this type of behavior are huge.