Throughout Lord of the Flies, we're led to believe that Piggy has never stood out for anything. He's weak, wears glasses, is overweight -- he's nothing like the athletic, charismatic boys he encounters on a regular basis. Ralph and Jack both are looked upon highly because of their demeanor and athleticism and strength of character, be it good or bad. In school, the only reason why Piggy may have received any special attention was his asthma. He would have needed special care should an attack occur. So, in the beginning, when he first meets Ralph, he says that he has it with that touch of pride because before landing, he stood out with that. Little does he realize that it is not necessarily a mark of respect but one of weakness, and it's his weaknesses that are his downfall in the end.
Piggy seems to have always been viewed as less than special and in some ways seems to have prescribed to this opinion of himself, as is often the case in those with low self-esteem. However, Piggy's asthmatic condition made him different from the other boys to some degree, and he probably exhibited a small amount of pride because he knew that his asthma made him special, even though it was truly a negative. Often, those who feel a desire to set themselves apart from those around them or to gain some amount of attention for themselves are willing to do so by any means possible, including engaging in behavior that results in receiving negative attention or bringing their "flaws" to the notice of others.