It originally means "to step on a land mine". It also means "to push someone's button" and it is used when you intentionally/unintentionally say something that offends someone.
Ken and Leo are gossiping about Meg.
- Ken : Do you know why Meg is grumpy today? I just asked her if she will take her boyfriend to the party tomorrow, but she ignored me.
なんで今日メグは機嫌が悪いの？明日のパーティーに彼氏を連れて来るか聞いただけなのに、無視された。 - Leo : Oh, I guess you pushed her button. She broke up with him a few days ago because he cheated on her.
あっ、地雷を踏んだかもね。彼氏が浮気して、数日前に別れたんだよ。 - Ken : You should've told me that before.
言ってよー。
Meg is about to ask Tom when he will finish his tasks.
- Amy : Are you going to talk to Tom?
トムと話すの？ - Meg : Yes. I'm wondering if he will finish his tasks in an hour.
うん。あと一時間で作業が終わるかどうか、気になって。 - Amy : Some colleagues asked him about the same thing. And he promised to wrap up those tasks quickly. I think that he is very busy and he is a bit irritated.
何人かが、同じ事を聞いていた。トムはすぐに終わらすって言っていたよ。忙しくて、ちょっとイライラしているみたい。 - Meg : Thank you for letting me know. I was almost about to do something wrong.
教えてくれてありがとう。もう少しで、地雷を踏むところだった。