For me, "getting triggered" means that something one of my senses (sight, smell, etc) noticed caused me to want to act in a negative behavior. Negative behaviors for me include self injury, substance use, isolation, avoidance, among other things.

The actual thing that causes the triggered feeling sometimes doesn't matter or even make sense. It may be something that has never triggered me before, or it may be something that I know triggers me (i.e. a particular cologne).

Honestly, it is almost impossible to write a post on here, that would not trigger anyone at all. Everyone's triggers are different, and again, some don't even make sense.

My advice:
There are basic topics that have a high likelihood of being triggering to several people, that should probably have a warning attached.
Ex. abuse of any kind, details of self injury, details of suicidal plans or actions, details of homicidal thoughts, any post that has an aggressive feel to it (usually rant/vent type posts)

This is totally my opinion and experience , so feel free to take it with a grain of salt.

Puck