That's how you know you've reached the limit, genius.
The obvious criminal cases are it. Everything else is allowed by definition. Its a freedom thing.
P.S. Let me make this really clear, because my Spidey-sense tells me you're trying to creep through the back door here: YES, it IS appropriate free speech to mock Muslims for their murderous barbarity, their enslaving of women and non-Muslims, and their efforts to destroy Western Civilization and replace it with Sharia. Got that?
Even if it enrages them to violence. In fact, ESPECIALLY if it enrages them to violence, so that we can use their violence as justification to go to global war with their damned murder cult and wipe them off of the face of the Earth once and for all.
I hope I've made myself clear.
I want absolute Freedom of Speech, because I want to know who the jerks are.