being hit by heaven and being struck by lightning, it means to die in a horrible way
Definitions (粵典–words.hk)
動詞
比喻不得好死 to die in a horrible way; literally: to be hit by heaven and struck by thunder (lightning)
我發誓:我投票俾佢嘅話,天打雷劈!
我发誓:我投票俾佢嘅话,天打雷劈!
ngo5 faat3 sai6: ngo5 tau4 piu3 bei2 keoi5 ge3 waa2, tin1 daa2 leoi4 pek3! I swear: If I vote for him, I'll get struck by lightning!