好为人师: be fond of teaching others; have a tendency to sermonize people; like to be a master to others; like to lecture other people; presumptuously to lecture people
班门弄斧: display one's slight skill before an expert; be conceited; display one's incompetence before a connoisseur; go to teach hewing to the god of carpenters; show off before a superior man; sho
不要班门弄斧: do not teach fish to swimdo not try to teach your grandmother to such eggsdon't try to teach fish how to swimnever offer to teach fish to swim
