If you called someone a crack addict and they were in fact a crack addict, that’s not really slander. If you did so in front of their boss with the intention of getting them fired, you may not fully be protected under “free speech” when he punches you in the jaw.
If he is not a crack addict at all, then that is generally slander. I’m no legal expert but I do believe intent and circumstances play into effect, such as if you guys were drinking in a bar and joshing around and you said it as a joke, versus telling the police he’s a crack addict. This relates to the impact your words have and your intent in saying them, in the first case there is likely no real impact as you didn’t intend to cause him harm, but in the second case you are willfully misrepresenting him to police [which gets you another charge] who may change their investigation as a result of your words.
So the question then becomes, why are you calling him a crack addict? What is your purpose? If your purpose is nefarious, it’s generally slander. If your words have a negative result for the person, it could be construed as slander. If the words are outright lies, you are not protected via free speech.