I watched the new Ian Hislop BBC series Stiff Upper Lip on iPlayer earlier (watch here, or see the programme website here), which was about how the stereotypical British character trait of a stiff upper lip is a relatively recent concept (he cited 15th and 16th Continental European visitors to England who were amazed at the abandon and gushing behaviour of the English). What's more, the phrase didn't even originate in Britain. The earliest recorded instance of its use, according to the OED, is in the newspaper The Massachusetts Spy in June 1815 in the sentence: "I kept a stiff upper lip, and bought [a] license to sell my goods." There's a citation from Uncle Tom's Cabin a bit later, too. The phrase became popular in Britain only towards the end of the 19th century.
The OED also has the related nouns stiff-upper-lippery and stiffupperlippishness (one word) and the adjectives stiff-upper-lipped and stiff-upper-lippish.