It's a joke from the season 1 episode. The Game.
Frank is trying to get Michael to go to sleep, and he does Peek-A-Boo in a scary way. Debra says "Oh, my God" and hurries upstairs. Ray and Robert could remember Frank doing that to them as kids, and Robert tells him not to do that again.

If you're gonna pretend to cut her hair, at least put some scissors in your hand!