red flag vs annoyance

red flag and annoyance both are nouns.

Word	Noun	Adjective	Verb	Adverb
red flag	Yes	No	No	No
annoyance	Yes	No	No	No

As nouns, annoyance is a hypernym of red flag; that is, annoyance is a word with a broader meaning than red flag:

Other hypernyms of red flag include annoying, irritation, vexation.

red flag (noun)	annoyance (noun)
something that irritates or demands immediate action	the act of troubling or annoying someone
a flag that serves as a warning signal	something or someone that causes trouble; a source of unhappiness
the emblem of socialist revolution	anger produced by some annoying irritation
	an unpleasant person who is annoying or exasperating
	the psychological state of being irritated or annoyed