We’ve had this too, the "oh poor thing" syndrome whenever our son would walk by.  We just explained to them that he is a normal kid just like everyone else, and that although we have to use a little extra caution with him during illnesses or injuries, we don’t plan to let it rule his life.  We also told them that we don’t want him to feel like he’s made of glass, or use his condition as an excuse for doing or not doing anything, so to please not moan over him when he’s around.  We’ve found that when we are asked about how he’s doing, a simple ’good’ is usually enough.  Going into excruciating detail about how difficult the blood draws are or the intricacies of his treatment only serves to make them feel sorrier for him, and he does not need or want anyone’s pity.  Our feeling on it is that this is the hand he was dealt, and it sucks out loud, but that is what is.  His life will not be worth living if it’s lived in fear, so we will allow him whatever experiences he feels he needs to have.  None of us know how long we will be here anyway; but kids like ours make sure that we never forget that. 

Best of luck to you with this.