You get better at this with age and experience.
The scene: the pizza place across from my office
The situation: I have placed my order and am now sitting at a table waiting for them to call me. I'm playing a game on my Nook.
A couple of older guys are joking with each other up near the counter, about 8 feet in front of me. I kind of glance up, smiling a bit because the comments were indeed funny, but then turn back to my Nook. Alas, one of the guys noticed this.
Guy: What're you doing? Texting?
Me (not looking up, neutral "not interested" voice): No, playing a game.
Guy (now standing next to me): What is that?
(It's the standard mahjong matching game)
Me (still not looking up, still using "not interested" voice): You match the tiles.
(I do not look up at any time through the following conversation.)
Guy: What's your name?
Now, at this point, I'm like, okay, dude is making a try, but the fact that I am answering in a monotone and not looking up should be all the hint he needs that I AM NOT INTERESTED. And -bam- I think, "I don't owe this guy an answer." This is not a revelation, but that I thought it before I answered is new.
Me, in a kind of snarky-but-not-unfriendly tone: I'm not tellin' ya.
(The eye dialect is there to help convey the tone and accent I was pulling out. I feel it was important to the situation. My voice went higher and hit the beat on "tell." The "I'm" is more stretched out, like "Aaaah'm".)
Guy: Hey, girl, I'm just trying to get something going here.
Me (same snarky/friendly tone): Ah know. That's why I'm not tellin' ya.
Guy (amused/impressed): Oooh! All right then.
He backs off. When I left the place, I saw him sitting with some friends, and I gave him a wave and said, "No hard feelings, man." Because hey, I won this round, and I believe in being a gracious winner. He replied, "No problem, love," but I could see he was not as happy about it as I was. But hey, dude, you stepped in it. Watch where you're walking next time.
It was impossible to keep the big-ass grin off my face for the rest of my time in the store, and all the way back to my office, and right now.