Three points:BonsaiK said:Quoting something from a TV show - ANY TV show - in conversation marks you out as someone who is unable to have original thoughts and think for themselves. Family Guy in particular cops a lot of flak because it is simply not that good a show - it's an inferior clone of The Simpsons in almost every single respect. The humour is duller and more obvious, the characters are poorer, it's not as original, it really is "The Simpsons for people who are too dim to understand the multi-layered humour of The Simpsons". So the general thinking of people is this: if you're going to be unoriginal and boring in your conversations, and crib lines from a TV show because you lack a personality, a sense of individuality or the ability to make witty remarks of your own, at least show people you have better TV-watching taste than Family Guy. That's the reason why people get criticised for it, as far as I can tell.
1) Originality is not the hallmark of quality. Those who hold out for a completely original show will be forever disappointed. One of the first things you learn when trying to engage books, television or movies beyond the surface is that all characters, plots, situations and even jokes have been done before and better. For further reading, see Joseph Campbell, Yahtzee on this website, George Lucas and the "Simpsons Already Did it" episode of South Park.
2) You call the humor of "The Simpsons" multi-layered, then say "Family Guy" is for the dim. On one level, yes, Seth MacFarlane is making dick jokes. On another, he deconstructing the last 30 years of pop culture, making ongoing commentary on contemporary morality and questioning the limits of basic narrative elements like character (On what level is Stewie a baby? An adult? In what ways is Brian a dog and how is he like us?) and plot (how much can events in a story stray from normal context or even causality?). It might not be your cup of tea, but anyone with an education and a critical eye can find a lot on "Family Guy" to stimulate some thought.
3) My wife and I quote "Family Guy" to one another to shortcut a few rather complex ideas in a few words. Example: when I am being particularly immature and needy, she will say, "You want some apple juice?" to indicate that I am displaying an infantile need for attention and, nevertheless, she is going to indulge me. Do we lack original thoughts because we engage in this "Family Guy" shorthand? No, we are acknowledging the inherent truth in a scene between Peter and Meg and finding it relevant to our own lives. This is the essence of artistic expression and criticism.
In other words: "Family Guy" does not lack wit. You don't know what wit is.