No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offence to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.
Analysis & Application
I PLEAD THE FIFTH is a common phrase, either used jokingly or in a legal case. This basically means that you don't have to answer questions without proper law backing.
This is applicable literally everywhere you don't want to answer a question, it's a common expression that people use.