1) Une fausse bonne idée: Something that seems like a good idea and isn’t (literally, ‘a fake good idea’.)
For example, I was out the other night with a group of old friends. We were sitting in a bar deciding what to order when Anna’s gaze wandered over to the next table. Two young men in the first flush of romance were sucking a raspberry pink cocktail through two straws from an improbably large glass. “That looks good!” she said. “Why don’t we have one of those?”
To me that was your quintessential fausse bonne idée. Indeed, when we all thought about it we knew instinctively that what we were looking at was a bad idea disguised as a good one and so we all ordered Mojitos.
2) Une cochonne. This is a useful term used to describe an adult woman (any age) who seems openly to like sex. Even though the English translation for this word would probably be “a filthy or loose woman” it is important to point out that in French Cochonne is not a term of abuse even though a cochonne is obviously a female pig (the proper French word for sow is Truie). NB: The masculine version, cochon, is a term of abuse.
It can also be used as an adjective:
a) une sieste cochonne (a dirty afternoon nap)
b) une robe cochonne (a revealing, or rude dress)