The meme refers to the old adage "C lets you shoot yourself on the foot. C++ lets you shoot both feet and gives you a shotgun to do it" - referring to the how C allows you to perform memory-unsafe operations (causing corruption, or worse, security vulnerabilities), and C++'s complexity, potentially obscuring such unsafetyness.

Rust's memory safety tries to save you from doing (un)intentional bad stuff, by giving you compile-time errors. It's also the bane of everyone so used to C/++'s ability to just pass around and modify whatever memory they want.