Basically you're looking for funny immature little things people say right? Well, a lot of my friends say this and it was pretty funny because it's unexpected, but it gets old since they always say it to me. I just ignore them now. It could be a nice one timer though:
Them: <asks a question>
You: Because you touch yourself at night.
________________________
Other stuff I say are like:
Them: What time is it?
Me: Time for you to get a watch.
Them: Where are you going?
Me: . . . whereever God takes me.
Them: What's that for? (refering to project or something)
Me: Top secret. If I told you . . . I'd have to kill you.
So those usually get everyone at least smiling and clear up the mood. What follows are kind of dark.
_________________________
Them: <starts to talk about problems>
Me: hold on a sec, let me get comfortable
Then I put my head down and say, "ok I'm ready."
__________________________
I tend to stand up for people and this is some stuff I say in those situations. Shuts them up quick and all the bystanders too sissy to do anything look up to you real fast.
Them: <someone trying to be funny, but is failing miserably by trying to be a jackass to people they think are lower>
Me: Dude, are you still talking?
Them: <making fun of people>
Me: **sneeze** whew!*sniff* Sorry, but I'm allergic to *******s.
Ok so basically sometimes Im really cynical and my darker side comes out. Other times, I just use stuff from movies you know like the "top secret..." example.