Literally a public urinal in most major European cities, but sometimes a creative way of saying you are pissed off, or pissed off at someone, or someone is an idiot; sometimes used as an exclamation.
A more sophisticated way of calling an individual a pussy. It can also be used more publically than 'pussy' since many people are still ignorant of its meaning.
1st Guy: Adam, I cantbelieve you havn't talked to that girl yet. You're such a poussoire.
Group: POUSSOIRE!!!