When creating a histogram, the practice of choosing less bins than you have distinct values, thus "double-binning" (at least) two distinct values into a single bin.
S: "Man, this histogram looks odd. Why is there a spike at either end?"
M: "Are you double-binning?"
S: "Ahhhhhhhh"
Double-4C: Person who, in relation to the other person, has zero parents, zero grandparents, zero great-grandparents, zero great-great-grandparents and four great-great-great-grandparents in common.