Can anyone play dictionary definition one-upmanship."An extreme form of patriotism marked by a feeling of superiority over other countries". Which is exactly what I've said:
Here's my contribution, an extract of one of several definitions from what is generally regarded as the English language reference dictionary, the full OED, :-
I've added the bold to stress the Brexit relevance, but the small text is as per the OED itself.1.
a. Advocacy of or support for the interests of one's own nation, esp. to the exclusion or detriment of the interests of other nations. Also: advocacy of or support for national independence or self-determination.
Whereas patriotism usually refers to a general sentiment, nationalism now usually refers to a specific ideology, esp. one expressed through political activism. In earlier use, however, the two appear to have been more or less interchangeable.
Nothing in that requires a feeling of superiority over other countries.
The problem with dictionary definitions, or perhaps with English as a language, is that they are numerous and the applicable definition has to be derived in part from context, and perhaps in part from the inferred intent of whoever used the word or term. Even the OED, however highly respected, is not an official arbiter of meaning.
Oh, and I've not given a link as it's a subscription service to the online version. I don't know what, if anything, is available without subscription.