One of the pubs I go to in Margate has these awful seaside postcard illustrations on the walls of the toilet. These are pretty tame, usually, though some of them make reasonably explicit references. They usually rely on double entendre of some kind for the joke. Here's one where the joke relies on the way that the meaning of adjectives changes in different contexts:
Good is a particularly fuzzy word. What does it mean? All we can really say is that it has some positive meaning (and even 'positive' is a bit vague). The rest, nearly all of the meaning, has to come from context. This is known as being 'underdetermined'.
Doctor Who uses this to good effect in one episode: the Doctor (played by Peter Capaldi, I think, or maybe it was Matt Smith - one of the modern ones, anyway) says early on that there is no such thing as a good dalek, meaning that they're inherently evil beings. At the end of the episode - spoiler alert - the daleks call the Doctor himself a 'good dalek', meaning that he is good at being a dalek. The difference lies in the application of the word good to some aspect of dalekhood, in which case it means 'unfeeling', 'ruthless', efficient', or whatever, or in treating it separately and giving it whatever meaning the word has when applied to animate entities more generally ('kind', 'well-meaning', etc).
The woman in the cartoon says I promised Mummy I'd be good... was I?. It's the same thing as the Doctor Who example, more or less, but good means different things again. What she promised her Mummy was that she'd be good in the sense of the term as applied to the behaviour of daughters on a night out: polite, sober, and most importantly, chaste. What she's asking the man is whether she was good at a particular activity: in other words, did she perform well at it? This conflicts with the crucial parts of how she promised her Mummy she'd behave, but it doesn't mean that good has conflicting meanings. It just has almost no meaning without a knowledge of what it applies to.
How you interpreted the title of this post out of context might give you some idea of how filthy a mind you have.