Inform Rudolphus that his wife is cheating on him with the Dark Lord
Tell Bellatrix she needs to fire her hair stylist
During supper, say that the food must taste better than in Azkaban
Tell her she closely resembles that Muggle "Helena Bonham Carter"
Suggest she add more color in her wardrobe, such as fuchsia and chartreuse
Put pink dye in her shampoo (if she uses it), and when she accuses you, say she looks like her darling niece, Tonks.
Confiscate her wand; claim it's a Ministry decree that she has to spend a month surviving in the Muggle world