NO YOU CAN'T HAVE MY DAMN NUMBER

I often find I have a lot of trouble saying 'No' to people. I don't mind going out of my way to help someone and other times I'm scared I'll hurt the person's feelings by saying no. It may have something to do with me not having a a whole lot of confidence.
In particular, when a guy asks for my number and I really don't want to give it to them, I end up saying yes instead of "Well I have a boyfrand." (LIES) I want to slap myself in the face afterwards because

1. For leading this guy on and not lying to him
2. I may end up getting spammed with hundreds of text message and calls. 

I end up writing "Do not answer" or "Creep is calling" in the name field.
I'm also a horrible liar. Not all the time, I can make up a pretty good story but it isn't hard to tell when I'm lying. Often you can tell by the look in my insanely huge eyes or I pull a face which is similar to this...........

There's a gay man at Tafe who has taken a liking to me just because I was nice to him once. He almost seems to follow me around since I see him a lot. I swear I had never seen him before I met him and now I see him more than I see my actual friends. He doesn't seem to notice that his constant presence in my personal space, the way he flamboyantly runs up and hugs me, makes me uncomfortable along the strange sexual things he says. Now the fact that he's gay has nothing to do with why I'm uncomfortable. (that's discriminative and wrong) though might I mention that this guy has a daughter and he is in his 30's. YEAH. He has asked for my number and even my home phone and according to me and anyone else he asks, I don't know my 'new number' and neither does anyone else.

After that I felt no more could be done about the situation and before my phone decided to grow legs and crawl out of my bag shouting "HEY DICKHEAD, SHE'S LYING", I turned around and ran like a bitch. I can only assume he stared after me as I ran, most likely confused as ever.

I suck as a person