Sci Fi Aliens

One thing that's bothering me today is the trope of aliens calling humans or other organisms "carbon based lifeforms" that is found in media. This is annoying me because I was under the assumption that all known life contains carbon. So my question is.. what do they know that we don't? What are they made out of? And why are they acting like they're superior, or surprised, or that categorizing something as carbon-based is effective?? By scoffing and saying "oh, you're a carbon-based lifeform" that's, it's just stupid. The concept is stupid. I'm a carbon-based lifeform. Do you know what else is? A fucking aloe plant. Come on. Like genuinely, what are these aliens made out of? Now I understand why humans want to dissect aliens so bad! This is just one of my many gripes with alien representation in science fiction media.