My first community interactive event was painting with soap bubbles.I added clothing dye to large pans of bubble solution and made giant bubble wands out of coat-hangers.
Then I took the set-up to the park and started catching bubbles that Elana made with a huge piece of foam board. When the bubbles landed they would leave colorful splats, wavy circles, and drip lines. When people saw the bubbles and the bright colors on the board they wandered over and we invited them to join in.
We got a couple of waves of little kids. They had difficulty making the giant bubbles. In future, I would probably have more small bubble blowers (I only had two) and smaller pieces of foam board so that the kids would have an easier time of it. But they had a lot of fun popping the bubbles.
We provided smocks, safety goggles, and gloves, but they kids wouldn't always use them, especially the gloves. Smocks were fairly accepted.
Because there is no way to control where soap bubbles will fly, painting with them is an inherently team-building process. One person makes the bubbles, and another person holds the foam-board and tries to catch them.
People seemed to meet each other and make connections.
After 2.5 hours we had gotten around 25 people from children to retirees who participated, and many who stopped and watched. All in all it went well.
The completed products
Sometimes bubbles would leave nice circles with wavey soap-oil patterns.
If you're interested in seeing more of this sort of thing, my inspiration was Free Style Arts Association in New York.