Tell me just one sentence that you always use in your daily life :)
I'm married, so the one sentence I use every day is, "Yes, dear, whatever you say, dear."
"Oh my dog" :)
Just a word for me: "Perspective". Anytime, I start to lose it, I bring it back, even if partially by telling myself this word. Then I stand back, look at the situation, and reassess it. It usually looks different enough to make me realize it was not as serious as I thought and I shouldn't sweat over it so much. And when I finally stop sweating, I can smell the roses:-)
Hmm....it depends on who I talk to. Oh! I often say: "I'm knackered (tired) today", but....em...maybe this one isn't so useful for you. ;-)
I guess since I spend most of my time with my husband, I normally end up saying things like: "Do you need anything from the kitchen/bathroom/etc?" or "Are we going anywhere else today?"
If you want a generic answer, then I guess pleasantries are the thing I use the most on a day-to-day basis: hello; how are you?; The weather is nice/awful, today; excuse me; please; thank you; no problem; goodbye; etc.
Never say never!
Don't give up!
Just a little more won't hurt. ;) *nom, nom, nom*
Put the kettle on.