The tu quoque fallacy is modeled on a clean hands defense.
Willy W: "here, try one of these."
Scarlett B: "what are they?"
Willy W: "Rainbow Drops. Suck 'em and you can spit in seven different colors."
Violet B: "spitting's a dirty habit." **picks nose**
Willy W: "I know a worse one."
Tu quoque is a red herring. The log in Violet's eye does not remove the (as is eventually revealed) forest from Mr. Wonka's. Spitting is a dirty habit, even if a hypocrite points it out.
A related fallacy, one that may already have a name for all I know, is that a third party jurist is obliged to consider the moral failings of others before criticizing someone. The "third party" bit is an important distinction, otherwise it would be the infamous "whataboutism" of Soviet propaganda as you recall from the official responses to Chernobyl ("but your capitalist Three Mile Island also poisoned your people."), Stalin's purges ("are you not still lynching your Negroes?"), or more recently, the Kursk ("your Scorpion and your Thresher also sank").
To pick a totally non-controversial example of the illud quoque fallacy, flapjaw pundits stateside who criticize Israel's foreign policy might run afoul of someone who claims that you can't critique Israeli political elites while there are Islamic militants running amok in the North, brutally executing innocents.
It's a red herring argument, and it's plastered all over i.a. the goings-on in Missouri right now.
Talk is exchange. Some of it is, anyway. Some of it is pollution. Fallacies of moral equivalence introduce noise into what otherwise might be useful signal. Be euvoluntary; resist the temptation to drift into irrelevant moral equivalence.