Triggering is not a joke.

Before you joke about 'triggers' or people getting 'triggered', please educate yourself as to what the word 'trigger' actually means.

A trauma trigger is an experience that causes someone to recall a previous traumatic memory, although the trigger itself need not be frightening or traumatic and can be indirectly or superficially reminiscent an earlier traumatic incident.

This means that a trigger is something that sets off a flashback or a memory, which transports someone back to the event of their original trauma.
Triggers can be everywhere, and affect tens of millions of people. Before you make jokes that could be harmful to people you know and love, please consider the effect of your words.

As a side note, 'triggered' is not, and has never been a synonym for 'offended'. They have completely separate meanings.