>>42469025
I'm not sure if this is exactly where it originates, but it's used quite frequently in The Clone Wars. Clones and many others were calling droids clankers at least as far back as 2008, and yes it was often used derogatorily. The modern political nutjobs and newer generations have seemingly taken a liking to the word, and are using it unironically to insult AI and robots across the globe.