I told hubby that I would think after 3 years of this he would get the hint that I didnt hear him. I have even tried variations of this, instead of WHAT or HUH. I will flat out say "what did you say?" and he will still reply with chartreuse squirrels.
Egads that must be frustrating! Dark Boyfriend (and others) only do it about 1/4 of the time, luckily.
Its very frustrating! And to be honest, I think he does it because he knows it drives me bonkers.