mom'sfolly :
I think you have to be rude and confrontational in this situation. Polite and nice are just going to get you more of the same. Unfortunately, this could escalate. A forceful, "I'm not interested, please leave me alone", might help. Every time he bumps or touches you, say clearly, and loudly "don't touch me". I would also approach the professor of this class and the lab proctor. Tell them that this guy is making you uncomfortable, won't leave you alone, and won't take no for an answer. They will have to respond, as what he is doing has crossed the line to harassment. They can help you, and should help you.
Don't smile, don't say hello, walk away when he approaches and if he touches you, go with the bloody stump comment. Say "no" frequently, forcefully and without any other interpretation. No, leave me alone, I'm not interested, don't touch me, repeated as neccesary. If it continues, report it to someone.
You have already told him you are not interested. Tell the class and lab teachers, and ask that they change HIS seat; you should not be penalized for his behavior. Report his behavior to the campus police--he may have a record of stalking others. He may not, but better to be safe. Return the chocolates and once again tell him that you are not interested. Most guys will accept "no" if clearly stated (too many girls tend to "let them off gently," so gently that they don't receive the message. You have already made yourself clear, and it was ignored. At this point is IS stalking/harrassment.
I think you have to be rude and confrontational in this situation. Polite and nice are just going to get you more of the same. Unfortunately, this could escalate. A forceful, "I'm not interested, please leave me alone", might help. Every time he bumps or touches you, say clearly, and loudly "don't touch me". I would also approach the professor of this class and the lab proctor. Tell them that this guy is making you uncomfortable, won't leave you alone, and won't take no for an answer. They will have to respond, as what he is doing has crossed the line to harassment. They can help you, and should help you.
Don't smile, don't say hello, walk away when he approaches and if he touches you, go with the bloody stump comment. Say "no" frequently, forcefully and without any other interpretation. No, leave me alone, I'm not interested, don't touch me, repeated as neccesary. If it continues, report it to someone.

You have already told him you are not interested. Tell the class and lab teachers, and ask that they change HIS seat; you should not be penalized for his behavior. Report his behavior to the campus police--he may have a record of stalking others. He may not, but better to be safe. Return the chocolates and once again tell him that you are not interested. Most guys will accept "no" if clearly stated (too many girls tend to "let them off gently," so gently that they don't receive the message. You have already made yourself clear, and it was ignored. At this point is IS stalking/harrassment.