班门弄斧 (Bān mén nòng fǔ): to display one's slight skill before an expert
班门弄斧
to display one's slight skill before an expert
Showing off your axework outside the gate of Ban the master carpenter. Usually said about oneself, as an apology before speaking up in front of someone who knows far more.
The same saying in Japanese: 釈迦に説法