Avoir la gueule de bois

Let's say, you go to a Beaujolais Nouveau party with some friends on Thursday 18 November. You may have quite a lot of that Beaujolais. You're not sure how you get home afterwards, but you do. You wake up on the couch the next day and notice you're still wearing the previous night's clothes. You have a splitting headache and can barely utter a word because your mouth feels as dry as wood. In short, you have la gueule de bois, otherwise known as a hangover. Of course none of that will ever happen to you; this is pure fiction.

The expression literally translates as to have a wooden mouth, and means that you got drunk and are now feeling the aftereffects.

La gueule is the muzzle or the snout of an animal in English. But if applied to a human being, it refers to the mouth, the face or the head in French, and is usually an insult. In fact, if you hear someone say, Ta gueule! you may wish to run away. Fur is going to fly. It is equivalent to shut up! with a swear word in the middle, so as to sound really, really angry. You will also hear the verb gueuler as slang for to yell, to shout.

Other slang phrases that you'll hear frequently and want to use with caution are:

se casser la gueule - to break one's neck, to fall apart, to fail

(In proper French: se casser la figure, tomber, échouer)

casser la gueule à quelqu'un - to beat the hell out of someone

(In proper French : frapper quelqu'un)

faire la gueule - to make a face, to be in a bad mood, to sulk

(In proper French: faire la tête, être de mauvaise humeur, bouder.)

Contrary to the above, the expression avoir la gueule de bois is perfectly acceptable in everyday language - it isn't rude and there is no insult implied. Alternatively, you could say avoir trop bu - having had too much to drink.

Another derivative of gueule that you can use freely is un gueuleton - a big meal, a feast. This one too has transferred into everyday French with no negative, or even slang, connotation.

Origin

La gueule de bois seems to go back to the 18th century as a metaphor to describe that uncomfortable situation of waking up only to have to peel apart your eyelids and then discover someone must have been sandpapering your mouth during the night. While the expression originally described that sensation of dehydration caused by excess alcohol in the system, it now refers to all symptoms relating to the morning after a night of over-watering.

Examples

Ne bois pas trop de champagne, tu ne veux pas avoir la gueule de bois demain.
Don't drink too much champagne, you don't want to have a hangover tomorrow.

Il existe de nombreux remèdes soi-disant efficaces contre la gueule de bois, allant d'une consommation supplémentaire d'alcool à manger de la pizza froide, mais peu sont prouvés scientifiquement.
There are many so-called cures for a hangover, from drinking more alcohol to eating cold pizza, but few have any actual scientific basis.