Let them perform. Let them lie. Let them think they won. Anything built on dishonesty eventually falls apart on its own. You don't have to expose anyone. time has a way of doing that for you.
There's something seriously wrong with someone's spirit if they gain pleasure from humiliating, embarrassing, slandering, and belittling other people for entertainment.
Know the family your person comes from before saying “I do.” You might be marrying into a generational curse. It can work with a curse breaker, but not a curse keeper. If no one in their family has maintained a healthy relationship, ask serious questions.