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1. To cause some explosive device to detonate. A noun or pronoun can be used between "trigger" and "off." The jet drops the bombs from above and then triggers them off remotely. The construction activity triggered off a landmine that had been buried since the second World War.
2. To cause some severe or extreme event, condition, or situation to begin or occur. A noun or pronoun can be used between "trigger" and "off." The results of the election triggered off nationwide protests. Doctors still aren't sure what caused my collapse, but they think that it was probably stress that triggered it off.
3. To cause someone to become angry or irritated. In this usage, a noun or pronoun is used between "trigger" and "off." I still don't know what exactly triggered Tom off, but he's been in a foul mood ever since. Our mother was prone to angry outbursts, so we always had to be careful not to trigger her off.
trigger someone off
to cause someone to become angry. (Fig. on trigger something off.) Your rude comments triggered her off. Your comments triggered off Bob's temper.
trigger something off
to set something off, such as an explosion. We were afraid that the sparks from the engine would trigger an explosion off. The sparks triggered off an explosion.