Besides the well-known term used for the description of something that amplifies people's voices (or grunts) with the intent mainly being on annoying everyone in a 1 mile radius.
To the same effect, a megaphone is also a person that thinks the person on the receiving end of the phone conversation must be deaf, or they are at a rave, so their voice must overcome all other noises. No matter what, their grating utterances find their way into your brain, often causing it to melt completely, or if you are lucky, cause your cells to spontaneously combust. If you are not lucky, then you are left alive, and must live with these people until you are so old that you do go deaf, or fall down a stairwell and (due to the immense friction created), spontaneously combust.
You will know these "megaphones" when you see them, as they talk rather loudly (even when off the phone), and often resemble small useless animals. Like poodles. They are mainly self-important individuals that think they are the sole creator of the universe, and of course, their opinions are fact, up is down, and left is actually right.
I have a sneaking suspicion these devils are somehow connected with the big brother.
There is no cure, short of eliminating all said individuals, and or taking out their vocal cords (or tongue).
"Oh crap, I just got done talking to a megaphone, and I think she blew my zarking eardrums out! aieeee!"