How to nicely refuse to give your phone number?

Give him a fake one.

google voice or skype number...
They can always leave a message, and you can forward calls to your cell, but you never give out your cell...

You just say no. Just make sure you don't change your mind. I've noticed that as "rude" as girls seem when they refuse to give us their number, they take a lot more offense when they want to give it to us for whatever reason (after saying NO the first time) and us guys reject them. They stay sore for a long LONG time and make us seem like the bad guys. I just tell her that the opportunity has passed and if she is nice, I may ask again, but not to count on it. Some guys may not do this, but I feel like I have to take a stand against the whole "I changed my mind now, I'll honor you by giving you my number" thing.

Give him a FAKE Number..
most girls use this

Just be honest, polite and straight to the point. Lying or making false excuses would be poor and pathetic form . also imagine if you were in the opposite situation and how you would prefer to be let down?

put your head and arms down on the table and act really tired.

lie and say you already have a man

"No thank you," with a big shiny smile :D. They will question you, but just keep sticking to it. The smile is like a shield so they will not respond rudely.

Just say "sorry, I don't give my number out to strangers".

How to nicely refuse to give your phone number? You can't. Guys differ on what they consider nice. Plus there are guys who will consider the fact you rejected them rude.

How can I refuse when a guy asks for my number without looking like a snob? No.
Simple and short. You're under no obligation to please him or to ensure his feelings are not hurt.

"Sorry, I don't give my number to people I don't know" It isn't rude at all. Say it with a smile.