Just like yelling "fire" in a crowded theater (where there is no fire), sending someone a gif in the hopes that it causes a seizure is not protected speech. It's assult.
What if I post something that's just really offensive? I feel like we've entered a time where people would gladly see the First Amendment trodden over if it means seeing "justice" doled out to nasty people.
Your argument rests on something very different.
And your hypothetical situation isn't hypothetical – people who cyberbully others into committing suicide are certainly charged for their crimes.