By asking them to repeat themselves, you're forcing them to actually admit what they said and if they stand behind it. [substeps] Use a casual, innocent tone when you ask them to repeat themselves.
[header] How to tell someone that something they said offended you without being offensive yourself [title] Ask the person to repeat themselves. [step] This can be a great way to open up the conversation. Many people get away with saying offensive things because they assume no one will challenge them.