迅雷不及掩耳　

◎ 迅雷不及掩耳 xùnléi bù jí yǎn ěr

[sudden;as sudden as lightening;sudden peal of thunder leaves no time for covering ears] 雷声骤响,来不及捂住耳朵。比喻事情发生得过于突然,使人防不胜防