Noun
Synonym of labium superius oris
(The addition of quotations indicative of this usage is being sought:) (humorous, sarcastic, vulgar) Sarcastic or jocular response to an individual who has performed oral sex on someone.
Source: en.wiktionary.orgAnd though hard be the task, keep a stiff upper lip. Phoebe Cary
Sometimes you just have to bite your upper lip and put sunglasses on. Bob Dylan
I studied in Britain and spent great moments of my life there as a student living in Belsize Park. I admire the British trait of the stiff upper lip in the face of adversity. My wife studied in Britain, too, and both of us have many friends there. Asif Ali Zardari
Well, good-by, Uncle Tom; keep a stiff upper lip. Harriet Beecher Stowe
I couldn't wait to grow a mustache. I stopped shaving my upper lip the day I graduated from high school. John Oates
Keep a stiff upper lip. French Proverb