stick·ler 
/ˈstɪkəlɚ/ noun
plural stick·lers /ˈstɪkəlɚ/ noun [count] : a person who believes that something is very important and should be done or followed all the time
▪ an etiquette stickler — usually + for ▪ a stickler for proper etiquette ▪ He's a stickler for the rules.
▪ an etiquette stickler — usually + for ▪ a stickler for proper etiquette ▪ He's a stickler for the rules.
