Here's an idea that I did on another forum that we found amusing - may fall flat here. Basically we typed any old nonsense (as long it used proper words) to see how fast we could reach 100 posts.
One letter/word answers not allowed - can we quite funny reading the comments back afterwards.
Who's in?
How long before anyone notices?
No-one yet
Nope.
That should be copyrighted I think, never mind.
Anyone here?
You silly sod!
Don't mention the war!
Bugger, it's posting in the previous post
Idea abandoned 
I ditto Charisma:
Nope
c Godot Taxis
Mwahahahaha.
Agadoo
But why fish?
p'tang yang kipperbang
So I went to the travel agents and asked to book a flight at short notice. He said "you've just missed it."
He asked me how many apples there are in a barrel of grapes. That's when my foot exploded.
Two cats are sat on a sloping roof. Which one falls off first?
The one with the smaller meow / mu.
Mechanics, so...
I bought a watch off Salvador Dali... had to take it back.. it melted.
Interesting fact about watches...did you know that in adverts for clocks/watches, they always say the time 10:10, because its symmetrical and more pleasing to the eye, thus you're more likely to be drawn to it. That's the theory anyway.
More intriguing advertising talk soon...
If sugar could talk would it say it was sweet enough when asked if it wanted sugar in it's tea?
If a bird in a forest sang with no-one there to hear it, that'll be four pound seventy please.