It's Portland. Weirder and funnier things have happened.
Here is one of my favorites:
Massive and completely random pillowfight in downtown. It ended up being the largest event at Pioneer Square to date.
How about Zoobomb? Jump on a bike, any bike (though tiny minibikes are preferred), and race down the huge hill outside of the zoo. Ride the lightrail back up and repeat. Have a huge party.
Zoobomb bike pile outside of Powells and Rocco's:
Portland Urban Iditarod? This article sums it up nicely. PUI