Brown-nose came into use in the 1930s in the American armed forces, and is based on the image of the servile position of sticking one's nose into someone's anus. Surprisingly, though the idiom has a vulgar origin, the term brown-nose or brownnose is not currently considered to be a vulgar term.

Why do people have brown noses?

“Brown-nosers often suck up because they feel insecure or incompetent in their position,” says Marsden. “They use flattery as a way to hide their feelings and/or draw attention away from any inadequacies. Constructive criticism and reassurances can help them understand their strengths and weaknesses.”

What does it mean when someone says brown nosing?

to curry favor; behave obsequiously. verb (used with object), brown-nosed, brown-nos·ing. to seek favors from (a person) in an obsequious manner; fawn over. Also brown-noser.