Causing confusion or agitation; tending to make someone flustered or disturbed.
Present participle of 'fluster' (from Scandinavian roots via 1600s English). Standard '-ing' form used both as a gerund and as a descriptive adjective.
Notice how 'flustering' and 'flustrating' should mean the same thing, but 'flustering' is standard while 'flustrating' is informal. This reveals how language standardization works—some verb forms spread widely enough to become 'official,' while closely related ones don't.
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