Well, it goes both ways. The person who didn't credit/spaced/messed up code doesn't need to attack the person asking. However insulting someone to start with (as the person asking someone to credit) doesn't help... Neither does getting angry about it after being asked.
I know sometimes people read things different from how they were written. I think. "Hey, I noticed you were using my X, if possible could you please credit me so other people know where to find X?" Or something friendly and than someone attacks is just as unfair!
Overall... They are icons/codes/graphics... no need to be rude!