screaming 18 month old

so I have three kids 9,5,& 18 months but my youngest has started a habit of screaming in a shrill high pitch tone to get his way or when he's mad I am at a loss my oldest two have never done this ( my girls ) but my son does this everytime he disagrees with me how can I break this habit its so embarrassing when he does it in public because he literally sounds like a screamo singer or something everyone is always staring so I'm forced to leave with him.