I have all of these with incredible success. All are responses, but by using one of these I don't get sucked into a battle of wits with an unarmed person...
"OH... ?"
"Really."
"wow"
"huh" Or "Well, huh." I use this one a LOT. It works as well as work as it does at home. It works especially well when someone asks me "What do you think?"
and my all time personal favorite: "Let me know how that works out for you." I used that more with my kids than my spouse... and they will all tell you I used it WAY before Dr. Phil !
OH I almost forgot. A ready supply of Jujubees just in case I need to shove something in my mouth to keep me from saying something I really shouldn't.....