The most notorious example of Rob Liefeld’s artistic butchery is a pin-up he did of Captain America, in connection with the “Heroes Reborn” stunt that Marvel did in the 90s, letting Rob and Jim Lee take over a few of their flagship characters for a year.
Now, Rob admits that he screwed this one up, and acknowledges that Cap’s “boobs” are too big. But that’s not really the problem. The main problem is that his ribcage sticks out too far, and his pelvis and everything else are lined up under it, rather than still being connected to his spine. There were a few too many muscles, and his left shoulder really should be visible based on the angle of his chest. Thanks to that wonderful perfectly circular shield, which covers a multitude of sins, this was easy to fix. And took sympathy on poor Steve, and decastrated him, fixing (so to speak) an artistic sin that’s all too common.
The web site of la Asociación en Defensa de Liefeld y Otros (Association in Defense of Liefeld and Others) has an amusing deconstruction (or disrobing) of this image, suggesting that there is an anatomically… possible basis for it.