Someone that follows the Hitler's playbook on "how to become people's leader" - empty promises, demonising minorities, playing with people's emotions, developing capitalism and planning/executing politically-motivated coups.
Or in short
A play on words - a Hitler SIMP/Sympathiser; while they aren't literally Hitler, they are as close as someone living after the 2000s can be.
Elon Musk may not be a neo-Nazi, but he definitely acts like a Hitler-Symp!