I would suggest that the term "plastic paddy" compares with the term "coconut" in terms of potential offense caused.
They do not run in perfect parallel, but the thing they have in common is that they are both based on a false premisse i.e. that if someone of a particular background conforms to the wrong stereotype then they are not authentic.
The problem is that in order to differentiate autentic from non authentic one must assume that there is a right stereotype.
In fact, all stereotypes are inaccurate.
And on this basis it follows that your understanding is not that dissimilar to mine or anyone elses whose identity has become subject to the generalizations of judgemental observers.
It is important not to trivialise the experiences of others, whether by comparing them to your own experiences or by saying something about them "having a chip on their shoulder".