Definition of "snitches get stitches" [Urban Dictionary]:
A saying indicating that "snitches" or people who tell on others to authority will get stitches, resulting from some kind of abuse (physical or psychological) or misfortunes from fate (karma).

Example:
"Person 1: This employee did this indescribable thing that for sure is not true, have you seen this? He/She needs to go...
Person 2: You better watch out! Snitches get stitches!"