If you try to justify an act/belief by pointing out in others a similar act/belief, you are committing the fallacy of "two wrongs make a right." This fallacy can occur by suggesting "if others are doing it, I can too" (common practice). Another form of the fallacy occurs when you dismiss a criticism for your action/belief, because your critic is acting/believing in a similar way (you do it too).

Example:

1. I'm tailgating her, because she cut me off!
2. Big deal! Lots of people cheat too.
3. No one will expect me to be well mannered if he or she is not well mannered.
4. Why are my parents on my back about smoking pot? They are out every night getting drunk.
5. Why shouldn't I gossip about Laura Jane? You know she talks about us every chance she gets.
6. Jon: "Go easy on the scotch; you've had three shots already now." Jeff: "Oh sure, I'll put down my scotch when you put down that tequila. Lay off, man."
7. Lou: "It is immoral to use non-human animals for our own purposes. That includes eating animals, or using them for our clothing." Greg: "Okay, Mr. Leather Shoes, I hear you loud and clear. Let me eat my steak now, would you please?"
8. The city should not be singling out our company's problems at our chemical storage facilities, when the EPA records indicate the city's very own landfill has been cited as needing improvements. The council needs to clean up its own mess, before they go after us.
9. There's nothing more noble to behold than a sober mind in a healthy body, he used to tell me. I can't say it ever meant much to me though. I'm sure it didn't help that he was most insistent about this when he was roaring drunk.