For example: Ann Coulter opined that Barack Obama "felt perfectly comfortable throwing his white grandmother under the bus" in his speech on race earlier this spring, just to make a point. She's awful, and ordinarily I wouldn't dignify her with a link or even a mention, but this phrasing has been repeated ad nauseam on the internets on this topic. Just Google "threw his grandmother under a bus" to see what I mean. Or don't. Just take my word for it.
For another example: in the latest sordid craziness from Isiah Thomas, a 47-year old man--and it's just a coincidence, apparently, that it was a 47-year old man the police took to the hospital as a result of an accidental drug overdose-- claims it was his daughter, and not him, who needed treatment. "It wasn't his daughter," Harrison Police Chief David Hall told The Associated Press. "And why they're throwing her under the bus is beyond my ability to understand." (via The Huffington Post)
Boo to this horrible trope. I veto it with an override-proof veto, and also a presidential (President of Hightouchmegastore, LLC, thanks for asking) signing statement to the effect that if you're thinking about using this expression, don't even think about it. Just don't.