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In the song "Alice's Restaurant", when the singer describes being sent to the Group W bench (for those who possibly "may not be moral enough to join the Army") full of "mother-rapers, father-stabbers, and father-rapers", one of them asks him why he's there. When they hear his response "littering", they all move away from him on the bench. But he regains their respect by adding "And creating a nuisance".
In the Jonathan Coulton song "Re: Your Brains", the zombie singer informs his prospective victim that he and his colleagues are "not unreasonable" because while they intend to eat his brains "No one's gonna eat your eyes." Then again, they're saying this as a bargaining chip to convince him to let them in.
In Tom Lehrer's "The Irish Ballad", from Songs by Tom Lehrer, the little girl protagonist kills her entire family and then willingly admits to it when the police show up, because "lying, she knew, was a sin."
In Nick Cave's "The Curse of Millhaven," the protagonist is a self-confessed evil teenager, happily singing to police and townfolk about her outrageously long list of murders but is adamant though, she didn't kill the schoolteacher's dog: that was two other school-age psychos she has no respect for. To be fair, Lottie doesn't seem to have a lot of respect for much of anyone or anything. It could be read that she wouldn't have minded killing the dog but never got the chance, or that she'd gone beyond the point where animal cruelty was fun anymore. Mostly though, she just didn't want to be pegged for something she didn't do.
In the song Banned From Argo, some space pirates (or in the original rendition of the song, Klingons) planned to commence a raid on the titular shore leave planet. However, when they discovered the debauchery that a Starfleet crew (implied to be that of the Enterprise) is doing while on shore leave, they decided against raiding the shore leave planet and wanted to get out of there, implying that even they felt that what the crew on shore leave was doing was terrible.
They used to be angular, sneering and bald, If someone got killed even they were appalled, They never tortured, they never lied, They'd honor a promise if it meant they died.
The Barenaked Ladies' song "Bank Job" narrates the aftermath of a failed bank robbery. Midway through, we learn the reason everything went bad: one of the robbers panicked when he realized the bank's lobby was full of nuns.
"We're Crooks" (lyrics by P. G. Wodehouse) makes variations on this the punchline of each verse (e.g. "we've never been in Congress, for we draw the line at that").
The Irish protest song "The Patriot Game" explicitly condones shooting police officers, but draws the line at killing deserters.
Turns up in the lyrics of the Oingo Boingo song Little Girls, which is possibly about pedophilia:
Uh-oh! (Uhoh!) Take a second! (Take a second!) Uh-oh! (Uh-oh!) It's a mistake! (It's a mistake!) Uh-oh! (Uh-oh!) I'm in trouble! (I'm in trouble!) Uh-oh! (Uh-oh!) The little girl was just too little, too little, too little, too little, too little!