From entymonline.com entry for Dutch:

In Holland, duitsch is used of the people of Germany. The M.E. sense
survives in Pennsylvania Dutch, who immigrated from the Rhineland and
Switzerland. Since 1608, Dutch (adj.) has been a "pejorative label
pinned by English speakers on almost anything they regard as inferior,
irregular, or contrary to 'normal' (i.e., their own)
practice" [Rawson]. E.g. Dutch treat (1887), Dutch uncle (1838), etc.
-- probably exceeded in such usage only by Indian and Irish --
reflecting first British commercial and military rivalry and later
heavy Ger. immigration to U.S.

The Dutch themselves spoke English well enough to understand the
unsavory connotations of the label and in 1934 Dutch officials were
ordered by their government to stop using the term Dutch. Instead,
they were to rewrite their sentences so as to employ the official The
Netherlands. [Rawson]

Bulka