半路杀出个程咬金

bàn lù shā chū gè chéng yǎo jīnbanlushachugechengyaojin

1. lit. Cheng Yaojin ambushes the enemy (saying)
2. fig. sb shows up unexpectedly and disrupts the plan
3. sb whose presence is regarded as irksome

Study it in Yanamino