It's a lightweight craft used by douches to move around on the figurative conversational currents to spread their message of doucheness to new individuals who were blissfully unaware of their existence. It also has cupholders, which is the only redeeming quality of the douchecanoe.
"Wow, did you hear what Jim had to say at the party last night?"
"Yeah, he came from nowhere on his douchecanoe and made everyone feel uncomfortable."
new co-worker: Man, that guy seems great to work for the way he looks like Johnny Depp and wears sleeveless t-shirts.
worker: No way. He yells a lot and makes us cry.
new co-worker: Thanks for the heads up. What a Douchiano.
A particularly dangerous form of erupting douche that can go off without warning and expose innocent people for miles around to unsafe levels of douchery.
Oh man that guy on the train was such a fucktard , he managed to piss off everyone in the carriage, what a Douchecano