nothing feels good :(

Today was rather a good day. I spent good times with friends, we ate lunch. Then, i did my labs work, mostly worked well. I even went to gym but i couldn't do much. There were so many people in there.
But on the lot, i am not feeling good.Perhaps, it may be because I've met some people whom i don't like.
One more thing that's worrying me is that those guys in my class keep on bullying me. I don't know if it's natural of them. They are only joking i know, they do not mean what they say. As my friend says,"all boys are like this". I an wondering now, are boys/men not human being. Then, why do they just act like, well, sorry for the expression...
It is not acceptable to me now that they keep on talking to me like this, i should stop them but i do not really know how :(
I am too soft and i don't know, perhaps a little stupid too because i simply can't answer back and on top i never swear. My friends (female) say if i don't answer back, they will continue on like this but i believe it's the contrary.
On the whole, I am not being able to understand this kind of reaction and consequently react positively to this.
These people, i see them everyday, i can't avoid them...what to do :((