Make things spread fast: With a smile (or a scream)

A smile is among the most rapidly transmitted things I know. Laugh and the world laughs with you... smile and people smile back (they can't help themselves, as Herdmeister would aver).
We're monkey-see-monkey-do critters. Homo Mimicus. Things spread because we copy the monkey next to us. So spread with a smile?
One example HERD brings us of human-to-human transmission is the roadside floral tributes to road crash victims we now see so many of. I spotted a varient in New York last month: The bicycle the victim died on chained to a post on Broadway (I took a picture, right).
Now I read that the idea is being copied by fellow apes across the UK. They have been dubbed, Ghost Bikes.
This kind of spreading is very easy to spot (it's hard to miss a bike chained to a lamppost, hence the reporting in the mainstream press).
The idea is being easily and relatively rapidly copied. It is easy to understand the idea, and easy to create our own versions of it. (nb: The moment the Government makes a standard white replica bike to distribute to local authorities to attach to lampposts at accident black spots, the idea will be finished).
But perhaps there is already a brake on the pace at which ghost bikes can spread.

There's nothing funny about them. Nothing at all.

The things that get rapidly shared are not only those which can be easily copied and adapted (co-created) to suit the community we each interact with, they are also funny.

Smiling spreads fast. Laughter too. It's why the watching-tv-at-home belly laugh is a rare thing but the laughs-out-loud are two-a-penny when you're in a comedy club audience.

So, I'll stick with the idea that we pass on things that we think those we are passing on to will think is cool. Stuff spreads this way.

Bit if I think it's cool and funny stuff spreads way faster.

Perhaps it is simply because there are now three possible groups you will share with:
1. those you define as likely to think what you pass on is cool,
2. those you define as likely to think what you pass on is funny and finally,
3. those you define as likely to find it both cool and funny.

I'm guessing group three are the most likely to pass it on?

There's a darker flip: Fear and panic spreads rapidly through groups, too...

Ghost Bikes?