Very similar to a butt wagon, though a bit more oriented toward people who deserve a heavier term than butt wagon. A douche wagon can also safely be called a buttsnoipe, an asshaberdasher, a bunghole, etc.
{Seen on a drone flight video posted on YouTube:
While I was flying the drone, I "heard" a jingle for Bob's Discount Furniture but with altered lyrics.
To wit:
♪ Bob's Bob-O-Pedics ♪
♪ From your bµñg#Ø£€ to your ṕ€n¡s ♪
♪ Some douche wagon neutralised my socks!!! ♪
{~850ms delay}
♪ Bob's Bob-O-Pedics! ♪