One of the biggest difficulties I had with communication was my stutter. I first developed it the summer before starting junior high. At times it was almost impossible for me to speak clearly, unless I got angry, in which case my stutter would suddenly disappear. This speech impediment was quite persistent up until the end of high school when it mostly cleared up. I seem to relapse a little whenever I am anticipating a major change, like a new job, or starting a course of study.
And other peculiarity of my speech patterns is hyperlexia. I enjoy using my vocabulary, both for aesthetics and to convey nuance of meaning. However, this can act as a barrier to communication as not everyone is familiar with the same lexicon. It also lead people to presume that I was being haughty or pretentious, which was not my intent at all. Even when I think I am speaking normally people will sometimes tell me not to be so wordy. This is irksome to me.
Other problems I have had to tackle include the fact that I used to speak much too softly, so people could not make out what I was saying. I now project much more, but sometimes too much without realizing it. People used to have trouble understanding me on the phone (a major problem, as I was working as a receptionist at the time) which was likely the result of an unusual vocal cadence. For a time I would also laugh uncontrollably in conversation, which didn't go over well.
Finally; switching topics. My mind jumps around a lot. Somebody will say something which reminds me of something, which reminds me of something else, that brings to mind something really interesting that I just have to share, but that seems to come out of nowhere for the listener. Occasionally I will do this all on my own, monologueing and going off on rapid-fire tangents while some hapless soul smiles politely hoping that I will soon shut up. *sigh*