Also Known as: "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."
"You shouldn't eat meat."
"So? You used to eat meat."