How to deal with people who won't accept "I'm really busy I can't do that today"?

[an Imaginary cat owner]

someone who want a favor from you like "creating a facebook account" and you have a dead line to end a project and they won't leave or stop asking .
I usually repeat the phrase "I'm really busy I can't do that today" and then I would scream and shout to get them understand .

[runwithme.]

Just stop talking to them and ignore them! If they are rude enough to waste your time, then you need to put your foot down and let them know that you aren't going to put up with it.

[Antst]

Don't scream and shout. When you do that, you train people to think that you will give them attention if they keep bugging you. And to realize that they can irritate you if you tell them "no."

Say calmly, slowly, and briefly, "I can help you do that on XXXday." If they continue to ask, say, "I'm not available today, but I can help on XXXday." If they still won't stop, say, "I have said when I'm available. Feel free to take me up on that. I have to go."

[Juniper]

It's been my experience that saying "I'm really busy" sounds like a lie. So they probably think you're lying about it because it sounds so generic. It's also been my experience that if you are the type to normally do anything for anyone, they WILL take that for granted.

So instead of that, even though it's not really their business what you have to do, just tell them "Look man, I've got a million things to do today. I've got about twenty e-mails to answer, I've got a meeting with my department, I've got to put reports together and do some analysis for this project I'm working on, and that's all before lunch time. So I don't have time today."

And if they keep on, repeat yourself. Don't yell. Just repeat. Ask them to leave: "I really need to get to work. We'll talk later. I will SEE YOU LATER."

And tell this person no sometimes. Even when you don't have to.

[Kai]

I don't scream or yell, I just tell them it can't be done today, possibly tomorrow but there are no guarantees, and I concentrate on what I am doing, ignoring the person. If they continue to harp on whatever, I repeat that I'm extremely busy and if they want to take over some of my work, great, and then I'd have a little more time for things like FB accounts (or whatever). I point out that if they don't like it that I'm so busy, they need to take to the manager about hiring more people (no one ever wants to). They eventually go away because no one is paying any attention to them.