The Amazing World of Gumball - Season 4

When an unknown figure shows up and insults their Mom the kids are expecting a massive showdown but are surprised when Mom chooses the path of peace. Mom explains Yuki Masami's mother is an old school friend and repeatedly refuses to fight her despite further provocation. However when Yuki threatens to get Mom fired from her job Mom has no choice but to partake in a rematch of a karate match her and Yuki had fought as children.