It is not what we say that makes the difference it is what we do. Words can have power and meaning, but they gain this power by our actions or lack thereof. To tell someone you will do something and follow through with action will show you to be trustworthy, honest, etc. To make that same promise without action would show you to be the opposite.
You can say anything you want there is nothing to stop you, but something to keep in mind is the weight your words will have and what you do to prove them true or false.
What you say carries with it your emotions and thoughts all on its own. To viciously attack someone with words shows what you are thinking and until you do something to prove otherwise those words will stay.
If you have no intention of proving your words true then it would be best to say nothing at all.
"I say what I mean, and I do what I say." Vincent Hannah - Heat