M.L.
My Aunt had the same problem with one of her kids and the doctor told her to either blow hard and quick into their face or to splash a little water in their face. Either way it doesn't harm them but it gets them to stop and then you can help them realize their behavior is not appropriate. It has to be done EVERY time (sometimes several times in one setting) but they will get the hint when their screaming keeps getting interupted. I hope this helps you with your screamin' meme's! :)