It's simple, you reply with what the avatar of the person above you would say. Here's an example:
Person 1 [Has a Mario avatar]
Person 2 "It's a mia, Mario!" [Has a Needle from BFDI avatar]
Person 3: "Don't call me Needy!"
Person 1 [Has a Mario avatar]
Person 2 "It's a mia, Mario!" [Has a Needle from BFDI avatar]
Person 3: "Don't call me Needy!"