碰钉子 (pèngdīngzi) Being rejected / Being turned down
The character “碰 (pèng)” means to run into; “钉 (dīng)” means nail or tack
and “子 (zi)” is used as a suffix here.
Tā zài bànshì de shíhou pèngle dīngzi, huíjiā hòu xīnqíng bùhǎo.
He was in a bad mood when he came back home, for he was rejected when doing his job.