Hey dude
What I learned to avoid this type of situation is two things
1. Ignore him, as simple as that just ignore what he says, he keeps poking fun but unless he sees a reaction he'll eventually get tired of it, the more you show signs of anger or hatred the easier it is for him to poke fun. I used to be like you, i'm a junior, 16 1/2 and i only weigh about 135 at 5'7, so i'm not the biggest kid, but just don't worry about it. If you ignore him he'll stop.
2. This is more dangerous but I think you'll get a better reaction from this from the ladies
. Well anyway i found a really good mechanism for gaining popularity and respect is to be a wise azz or a smart azz whichever you prefer. Both are basically the same thing, with a slight difference, don't ask me what but you'd know the difference if the situation arose.
Here's what you do to become a smart azz. First loosen up, not everything has to be so serious. Second, are you loose yet? ok good now then look around you, stuff seen odd or funny to you? say it, say it LOUD, some of the best comedians whole skit is just pointing out the flaws in things. Do it small at first, just with your friends, don't say it to be mean say it as a joke, smile, just be cool about things. some people may get offended, but so what they need to pull the stick out of their azz and have fun. Thirdly watch stand-up on comedy central, they have great stand-up on friday nights, and they usually have something on at 7 est before the daily show (daytime viewing) comes on. Just watch how they make jokes, notice how they make things tie in together but still move away to start new topics, you won't have to do anything this complex, i just think its cool how they do it
, ok after you watch then learn how they make jokes, they observe the lighter side of life, they don't worry at all about what people think, and they can laugh at their own jokes.
Everything about your life will change, if you just calm down, relax, start breathing, and laughing. Because when you laugh your calm and its very good for you i hear. So whenever this guy is trying to be a wise azz, just say "Thats cool" is a sarcastic kinda way, and if that pisses him off, don't worry about it, if anything it'll throw him off because someone actually stood up to him. I hope this helps, if you have any questions feel free to drop me a line through e-mail or aim Neovincent13(@hotmail.com for e-mail) and if this wasn't the response you were looking for from your post, to bad, by the time you bulk up enough to kick this guys ass he'll be graduated because you gain roughly 1-2% strength a week (safely), i would not recomend roids for anyone, especially someone in HS. It won't help you bulk up quick enough without some serious side effect, so just take the buddhist way out, and enjoy life
(and no buddha wasn't fat when he was enlightened)