Custom field validation when current user equals a certain user

Is it possible using custom form validation to only allow a particular field to be edited by only 2 users?
I tried it on 1 user but it isn’t a valid expression. 
IF($USER!="609974980022b44f8ff9fc5e51b8516f", "You are not authorized to edit this field.") or maybe
IF {$$USER}.{emailAddr} = "john.Doe@mscdirect.com", true)

Any help is appreciated.