Logical Fallacy 3: Tu quoque (you too)

Tu quoque is Latin for "You too". So you justify your wrong action because someone else also does it. "My evidence may be invalid, but so is yours."

This is Part 3 in a series about Logical Fallacies. We are going through one fallacy at a time. There are many types of fallacious arguments. I'm going to try to explain them with examples then find ways to help you refute those arguments when they occur. Please comment or email if there's a particular fallacy you want me to tackle, or if you have success with refuting an argument using a good technique you can share.

My mother did this on the phone the other day. We were talking about religion when my mother told me I should start a cult or my own religion, because they make so much money. (WTF?)