The expression 'the Regina Georges of the world' means 'Regina George and all the other people who are similar to her'. We use this device when we are using a person's name to indicate a particular stereotype. 'The Regina Georges of this world' is a way of referring to all the people who behave in this way - Regina typifies, and is representative of, this type of behaviour. We use a definite article because it's a particular group of people. As for the apostrophe, it shouldn't be there - it should just be an 's' to indicate a plural.