The committee members were so baffled by the computer jargon used by the techies that they agreed one member would periodically ask, "Can you put that in plain English?"
The approach may have been simple and yet it worked. Most of us have the tendency to slide into language that shoots past many in our audience. That's why the expert who can translate the complicated or specialized into easy to understand terminology is so appreciated.
It's not talking down to people; it's talking to them rather than at them.
Professional jargon is an obvious danger but so too is any reference based on an experience or interest your audience might not share. Military and sports terms are prime sources of confusion but so too are fashion and literary references. Have you ever been frustrated by a writer who uses a quotation in another language and doesn't provide a translation?
That person may have a priority but clear communication isn't one of them. The unclear use of jargon is not quite as bad but it can run a close second.