I take it that you are not very old. (i.e. still in school) The problems your facing now have been faced by many people before hand so you don't have to worry about being alone through this.
Here's a little tip for you. Most of these people who shout off, puff out their chests, belittle other people etc.. Do it whether they are aware of it or not as a) a shield to hide the fact that in a fight they are scared too or b) as a tactical advantage, it's easier to win a fight if you are on the offencive rather than the defensive.
Agressiveness, be it through physical (including posturing) or verbal means will normally force the other person to become nervous, closed up. defencive, even passive Thus giving the agressor the advantage in a fight situation. Why is this? It's becuase it's easier to attack then to defend becuase in defending you are waiting for the agressors attack which could come from any one of his 4 limbs, in a number of different ways.
A couple of ways to help would be, A) take an agressive stance back, it might turn the tables on him. But the downside is, alot of these people are motivated by peer pressure and or girls on the top. (trying to look big and tough infront of girls) I have been in situations similar, When I got agressive back when he had back up (i.e. friends) the situation can turn ugly, not always, but you never know, so always prepare for the wost. But when I confronted them when they were alone, they would back down. Most people feel safe with backing. (it's natural) This way he might think twice about giving you trouble again, but you might also end up in a fight if he has his friends looking on.
b) Pre empt him. as he opens his mouth hit him as hard as you can. This will be the last thing he will expect you to do. In his mind he is the agressor all puffed chested and loud, you should close up and become timid. hitting him with shock him and will give you a window of oppotunity which will last a couple of second. My advice is don't stop hitting him. I don't care if you've done martial arts or not (and I am a martial artist) there are two things and two things alone that win the fight. 1) Determination, and 2) violence of action. You hit him, and you keep hitting him until you do not need to hit him no more. (I personally would suggest to a point where he is unable to get back up and attack as you leave the scene) This should also put his friends off as well from jumping into the mix.
If they do join in though... What can you do?? Well, your gonna get hit.. no if's or buts there. This is where being good at fighting comes in, although if it's not too many you should be okay. What you need to do is NOT WASTE TIME. do not sit there smacking sevel bells of shit out of one guy, while 4 others are coming up from the sides. You hit, hit hard, and make sure the guys down within a limited number of moves. 1 is best, stick to no more than three for times sake. Especially in a situation like this, take the fight to them, do not wait around for them to come to you, if you do that, you are not the agressor you are having to defend yourself which as I said puts you at a disadvantage. Be agressive, go to the nearest one to you and drop him, then turn and go at the next.
This is of course all fair and well. BUT, 1) it is hard to become agressive if your a regular joe. 2) a factor that you have out there, which we don't or at least didn't in the uk is. Sure you do them in. IN the UK they might come back and jump me. two which I would respond with taking them out one by one with a bat of some sort, and the situation evolves. In the US they are more likely to come back with a gun and shoot you.
So your best bet is to suck it up and walk way. no need to stand there and take it, just turn around and bugger off. Something when I look back to the past is. What was once taken as slander against a person was just some people having a bit of a good laugh. We all end up the but of peoples jokes from one time or another. learn to laugh along with it. When people like that make fun of you, it hurts. yet when your friends in later life do the same thing (and trust me they will do from time to time) it's taken light humouredly. The older you get these things will look different.
Now something you can do which is non violent, is, get some drinking behind you. then instead of smacking the crap outta them. pull out a bottle, and take them shot for shot.. till they can't stand no more. chances are they'll be like "woh man.. you can drink.... " and things might ease...
Wing Nut