A Buckle is not an ordinary buckle you use for a car its someone who is.... well lets just say a little bitch a buckle is a word for someone who is scared and cant fight.
TOM: "HEY YOU THAT KID TYM"
TIM: "TYM? OH YEAH I KNOW THAT KID HIS THE BIGGEST BUCKLE EVER"
TOM: "YEAH I KNOW RIGHT"