Jiggle physics are not sexist, but their most common usage in video games is. People demand games with lots of realism, so I am told, and people bounce, jiggle, and sway in real life, so yeah, people develop games with engines to capture that. This is fine. What is not fine is the immediate leap from "We can make things jiggle" to "BOOBS". Yes, breasts are definitely affected by motion, and one can concede perhaps bosoms are easily observed out of a great deal of things affected by inertia, but making video game characters with large breasts and impractical outfits which show off said breasts being affected by your great physics engine is sexist.