Just because someone doesn't understand what you're saying, does not mean you are not saying it clearly.
You may not be saying it clearly enough for that person, but it does not mean you deserve attitude and pissy tone because you're "talking in half sentences."
Sometimes a simple, "I don't understand what you are talking about, (are saying, are trying to say, mean....) will let the other person know that more information is needed. All of these things are nicer and don't put the other person on the defense. After the 3rd time of asking, then you might have the right to be annoyed and pissy... perfectly understandable to then flap your arms and raise your voice and blame me for not making sense.
So we're clear then.