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.
And your hypothetical situation isn't hypothetical – people who cyberbully others into committing suicide are certainly charged for their crimes.
Your argument rests on something very different.