a slur for robots

It gave me pause too. But, wikipedia again:

A pejorative word, phrase, slur, or derogatory term is a word or grammatical form expressing a negative or disrespectful connotation, a low opinion, or a lack of respect toward someone or something.

Not sure that’s what you meant though.

It is explicitly a slur. That’s the whole joke. People use it in analogy to the n-word all the time.