"Tu Quoque" means "you too," and this variant of the ad hominem is called the "You Too Fallacy."
This fallacy is committed when it is concluded that a person's claim is false because 1) it is inconsistent with something else a person has said or 2) what a person says is inconsistent with her actions.
This type of "argument" has the following form:
Person A makes claim X.
Person B asserts that A's actions or past claims are inconsistent with the truth of claim X.
Therefore X is false.
The fact that a person makes inconsistent claims does not make any particular claim he makes false (although of any pair of inconsistent claims only one can be true - but both can be false). Also, the fact that a person's claims are not consistent with his actions might indicate that the person is a hypocrite but this does not prove his claims are false.
- Bill: "Smoking is very unhealthy and leads to all sorts of problems. So take my advice and never start."
Jill: "Well, I certainly don't want to get cancer."
Bill: "I'm going to get a smoke. Want to join me Dave?"
Jill: "Well, I guess smoking can't be that bad. After all, Bill smokes."
- Jill: "I think the gun control bill shouldn't be supported because it won't be effective and will waste money."
Bill: "Well, just last month you supported the bill. So I guess you're wrong now."
- Peter: "Based on the arguments I have presented, it is evident that it is morally wrong to use animals for food or clothing."
Bill: "But you are wearing a leather jacket and you have a roast beef sandwich in your hand! How can you say that using animals for food and clothing is wrong!"
- Bill has borrowed Jane's expensive pen, but found he didn't return it. He tell's himself that it is okay to keep it, since she would have taken his.
- Jane: "Did you hear about those terrorists killing those poor people? That sort of killing is just wrong."
Sue: "Those terrorists are justified. After all, their land was taken from them. It is morally right for them to do what they do."
Jane: "Even when they blow up busloads of children?"
- After leaving a store, Jill notices that she has underpaid by $10. She decides not to return the money to the store because if she had overpaid, they would not have returned the money.
- Jill is horrified by the way the state uses capital punishment. Bill says that capital punishment is fine, since those the state kill don't have any qualms about killing others.
Barker: 166, Cedarblom and Paulsen: 155, Copi and Cohen: 97, Davis: 80