Would this be considered bullying? Girls Only?

I have a brother who is 12 and get picked on my this boy (16) in our neighborhood all the time....the kid gives my brother swirlies, pantses him, takes his money!! You name is he does it to my brother. My brother asked me to give that kid beef stew (it was from a movie, its where you have the kid held down and you put your right in his face and fart) I would consider that bullying...but because he does stuff like that to him, should I (big sister, 19) bully this 16 year old as retaliation? Another kicker...I'm actually friends with the bully's Mom and she said if I did that to him, she would not care in the least cuz she knows her son's a bully, lol.....whats ur opinion?